Polymerase-encoding nucleic acids and method of making and using them

ABSTRACT

The invention relates to thermostable polymerases that have polymerase activity temperatures in the range from 90° C. up to 113° C., such as those derived from  Pyrolobus fumaria , and to polynucleotides encoding the polymerases In addition, methods of designing new thermostable DNA polymerases and methods of use thereof are also provided. The polymerases have increased activity and stability at increased pH and temperature.

RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.09/656,309, filed Sep. 6, 2000 now U.S. Pat. No. 7,049,101, which is aContinuation-in-Part application of U.S. patent application Ser. No.09/391,340, filed Sep. 7, 1999, now U.S. Pat. No. 6,492,511 B2, which isa divisional of U.S. patent application Ser. No. 08/907,166, filed Aug.6, 1997, now issued as U.S. Pat. No. 5,948,666.

FIELD OF THE INVENTION

This invention relates generally to enzymes, polynucleotides encodingthe enzymes, the use of such polynucleotides and polypeptides, and morespecifically to enzymes having high temperature polymerase activity.

BACKGROUND

Thermophilic bacteria have received considerable attention as sources ofhighly active and thermostable enzymes. Interest in DNA polymerases fromthermophilic microbes increased with the invention of nucleic acidamplification processes. The use of thermostable enzymes, such as thosedescribed in U.S. Pat. No. 4,165,188, to amplify existing nucleic acidsequences in amounts that are large compared to the amount initiallypresent was described U.S. Pat. Nos. 4,683,195 and 4,683,202, whichdescribe the PCR process. These patents are incorporated herein byreference.

The PCR process involves denaturation of a target nucleic acid,hybridization of primers, and synthesis of complementary strandscatalyzed by a DNA polymerase. The amplification product of each primerbecomes a template for the production of the desired nucleic acidsequence. If the polymerase employed is a thermostable enzyme,polymerase need not be added after every denaturation step, because heatwill not destroy the polymerase activity. Thermostable DNA polymerasesare not irreversibly inactivated even when heated to 93° C. to 95° C.for brief periods of time, as, for example, in the practice of DNAamplification by PCR. In contrast, at this elevated temperature E. coliDNA Pol I is inactivated.

Archaeal hyperthermophiles, such as Pyrodictium and Methanopyrusspecies, grow at temperatures up to about 110° C. and are unable to growbelow 80 degree. C. (see, Stetter et al., 1990, FEMS MicrobiologyReviews 75:1170124, which is incorporated herein by reference). Thesesulfur reducing, strict anaerobes are isolated from submarineenvironments. For example, P. abyssi was isolated from a deep sea active“smoker” chimney off Guaymas Mexico at 2,000 meters depth and in 320° C.of venting water (Pley et al., 1991, Systematic and Applied Microbiology14:245). The hyperthermophile that lives at the highest knowntemperature, Pyrolobus fumaria, grows in the walls of hydrothermalvents, sometimes called smokers, through which superheated, mineral-richfluids erupt. Pyrolobus fumaria reproduces best in an environment ofabout 105° C. and can multiply in temperatures of up to 113° C., butstops growing at temperatures below 90° C.

The more common thermophilic microorganisms have an optimum growthtemperature at or about 90° C. and a maximum growth temperature at orabout 100° C. These less extreme hyperthermophiles can be grown inculture. For example, a gene encoding DNA polymerase has been cloned andsequenced from Thermococcus litoralis (EP No. 455,430). However, cultureof the extreme hyperthermophilic microorganisms is made difficult bytheir inability to grow on agar solidified media. For example,individual cells of the Pyrodictium species are extremely fragile, andthe organisms grow as fibrous networks, clogging the steel parts ofconventional fermentation apparatus. Thus, standard bacterialfermentation techniques are extremely difficult for culturingPyrodictium. (See Staley, J. T. et al. eds., Bergey's Manual ofSystematic Bacteriology, 1989, Williams and Wilkins, Baltimore, which isincorporated herein by reference.) These and other difficulties maypreclude laboratory culture for preparing large amounts of purifiednucleic acid polymerase enzymes for characterization and amino acidsequence analysis.

There is a desire in the art to produce thermostable DNA polymeraseshaving enhanced thermostability that may be used to improve the PCRprocess and to improve the results obtained when using a thermostableDNA polymerase in other recombinant techniques such as DNA sequencing,nick-translation, and reverse transcription. Accordingly, there is aneed in the art for the characterization, amino acid sequence, DNAsequence, and expression in a non-native host, of hyperthermophile DNApolymerase that are stable at extreme high temperature to eliminate thedifficulties associated with the native host.

SUMMARY OF THE INVENTION

The present invention meets these and other needs by providing anisolated nucleic acid having a sequence as set forth in SEQ ID NO: 1 andvariants thereof having at least 70% sequence identity to SEQ ID NO: 1and encoding polypeptides having polymerase activity at extreme hightemperature, such as temperatures of 95° C. to 113° C., for four or morehours.

One aspect of the invention is an isolated nucleic acid having asequence as set forth in SEQ ID NO: 1, sequences substantially identicalthereto, and sequences complementary thereto.

Another aspect of the invention is an isolated nucleic acid including atleast 10 consecutive bases of a sequence as set forth in SEQ ID NO: 1,sequences substantially identical thereto, and the sequencescomplementary thereto.

In yet another aspect, the invention provides an isolated nucleic acidencoding a polypeptide having a sequence as set forth in SEQ ID NO: 2and variants thereof having at least 70% sequence identity to suchsequences and encoding a polypeptide having thermostable polymeraseactivity at a temperature in a range from about 95° C. to 113° C.

Another aspect of the invention is an isolated nucleic acid encoding apolypeptide or a functional fragment thereof having a sequence as setforth in SEQ ID No: 2, and sequences substantially identical thereto.

Another aspect of the invention is an isolated nucleic acid encoding apolypeptide having at least 10 consecutive amino acids of a sequence asset forth in SEQ ID NO: 2, and sequences substantially identicalthereto.

In yet another aspect, the invention provides a purified polypeptidehaving a sequence as set forth in SEQ ID NO: 2, and sequencessubstantially identical thereto.

Another aspect of the invention is an isolated or purified antibody thatspecifically binds to a polypeptide having a sequence as set forth inSEQ ID NO: 2, and sequences substantially identical thereto.

Another aspect of the invention is an isolated or purified antibody orbinding fragment thereof, which specifically binds to a polypeptidehaving at least 10 consecutive amino acids of one of the polypeptides ofSEQ ID NO: 2, and sequences substantially identical thereto.

Another aspect of the invention is a method of making a polypeptidehaving a sequence as set forth in SEQ ID NO: 2, and sequencessubstantially identical thereto. The method includes introducing anucleic acid encoding the polypeptide into a host cell, wherein thenucleic acid is operably linked to a promoter, and culturing the hostcell under conditions that allow expression of the nucleic acid.

Another aspect of the invention is a method of making a polypeptidehaving at least 10 amino acids of a sequence as set forth in SEQ ID NO:2, and sequences substantially identical thereto. The method includesintroducing a nucleic acid encoding the polypeptide into a host cell,wherein the nucleic acid is operably linked to a promoter, and culturingthe host cell under conditions that allow expression of the nucleicacid, thereby producing the polypeptide.

Another aspect of the invention is a method of generating a variantincluding obtaining a nucleic acid having a sequence as set forth in SEQID NO: 1, sequences substantially identical thereto, sequencescomplementary to the sequences of SEQ ID NO: 1, fragments comprising atleast 30 consecutive nucleotides of the foregoing sequences, andchanging one or more nucleotides in the sequence to another nucleotide,deleting one or more nucleotides in the sequence, or adding one or morenucleotides to the sequence.

Another aspect of the invention is a computer readable medium havingstored thereon a sequence as set forth in SEQ ID NO: 1, and sequencessubstantially identical thereto, or a polypeptide sequence as set forthin SEQ ID NO: 2, and sequences substantially identical thereto.

Another aspect of the invention is a computer system including aprocessor and a data storage device wherein the data storage device hasstored thereon a sequence as set forth in SEQ ID NO: 1, and sequencessubstantially identical thereto, or a polypeptide having a sequence asset forth in SEQ ID NO: 2, and sequences substantially identicalthereto.

Another aspect of the invention is a method for comparing a firstsequence to a reference sequence wherein the first sequence is a nucleicacid having a sequence as set forth in SEQ ID NO: 1, and sequencessubstantially identical thereto, or a polypeptide code of SEQ ID NO: 2,and sequences substantially identical thereto. The method includesreading the first sequence and the reference sequence through use of acomputer program which compares sequences; and determining differencesbetween the first sequence and the reference sequence with the computerprogram.

Another aspect of the invention is a method for identifying a feature ina sequence as set forth in SEQ ID NO: 1, and sequences substantiallyidentical thereto, or a polypeptide having a sequence as set forth inSEQ ID NO: 2, and sequences substantially identical thereto, includingreading the sequence through the use of a computer program whichidentifies features in sequences; and identifying features in thesequence with the computer program.

Another aspect of the invention is an assay for identifying fragments orvariants of SEQ ID NO: 2, and sequences substantially identical thereto,and sequences substantially identical thereto, which retain the extremehigh temperature polymerase activity of the polypeptides of SEQ ID NO: 2(i.e., at temperatures of 95° C. to 113° C., for four or more hours. Theassay includes utilizing a polypeptide encoded by a nucleic acid havingat least 70% homology to SEQ ID NO: 1, and sequences substantiallyidentical thereto, or polypeptide fragment or variant encoded by SEQ IDNO: 1, to effect DNA polymerase activity in a PCR amplification atextreme high temperature for four or more hours and under conditionsthat allow said polypeptide or fragment or variant to function, and

-   -   detecting formation of an amplification product, wherein        formation of the amplification product is indicative of a        functional DNA polymerase polypeptide or fragment or variant.

BRIEF DESCRIPTION OF THE DRAWINGS

The following drawings are illustrative of embodiments of the inventionand are not meant to limit the scope of the invention as encompassed bythe claims.

FIGS. 1A through 1E show the nucleotide and deduced amino acid sequenceof DNA polymerase (1PY2) from Pyrolobus fumaria

FIG. 2 is a block diagram of a computer system.

FIG. 3 is a flow diagram illustrating one embodiment of a process forcomparing a new nucleotide or protein sequence with a database ofsequences in order to determine the homology levels between the newsequence and the sequences in the database.

FIG. 4 is a flow diagram illustrating one embodiment of a process in acomputer for determining whether two sequences are homologous.

FIG. 5 is a flow diagram illustrating one embodiment of an identifierprocess 300 for detecting the presence of a feature in a sequence.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to DNA polymerases and polynucleotidesencoding them. The polynucleotide encoding SEQ ID NO:1 was originallyrecovered from a genomic gene library derived from Pyrolobus fumaria.This 2412 base pair polynucleotide encodes a protein having a deduced803 amino acid sequence (SEQ ID NO:2).

The present invention provides purified thermostable DNA polymerasesthat catalyze DNA synthesis by addition of deoxynucleotides to the 3′end of a polynucleotide chain, using a complementary polynucleotidestrand as a template. An exemplary purified enzyme is a polymerasederived from an organism referred herein as “Pyrolobus fumaria,” ahyperthermophile that grows in the walls of hydrothermal vents throughwhich superheated, mineral-rich fluids erupt. Pyrolobus fumariareproduces best in an environment of about 105° C. and can multiply intemperatures of up to 113° C., but stops growing at temperatures below90° C. This exemplary enzyme (shown in FIG. 1B) may be used topolymerize DNA where desired. The polymerase enzyme of the presentinvention has a very high thermostability and processivity. ThePyrolobus fumaria polymerase remains robustly active even after four ormore hours at temperatures as high as 95° C. to 113° C. Therefore it isparticularly useful and reliable for PCR amplification of templatemolecules greater than 20 kb in length and/or having a GC content ofgreater than 90%, templates which typically require longer amplificationtimes and higher temperatures.

One property found in the Pyrolobus fumaria DNA polymerase enzymes, butlacking in native Taq DNA polymerase and native Tth DNA polymerase, is3′ 5′ exonuclease activity. This 3′ 5′ exonuclease activity, which iscommonly known as a “proof-reading” activity, is generally considered tobe desirable because misincorporated or unmatched bases of thesynthesized nucleic acid sequence are eliminated by this activity.Therefore, the fidelity of PCR utilizing a polymerase with 3′ 5′exonuclease activity (e.g. the invention Pyrolobus fumaria DNApolymerase enzymes) is increased. However, the 3′ 5′ exonucleaseactivity found in DNA polymerase enzymes can also increase non-specificbackground amplification in PCR by modifying the 3′ end of the primers.The 3′ 5′ exonuclease activity can eliminate single-stranded DNAs, suchas primers or single-stranded template. In essence, every 3′-nucleotideof a single-stranded primer or template is treated by the enzyme asunmatched and is therefore degraded. To avoid primer degradation in PCR,one can add phosphorothioate to the 3′ ends of the primers.Phosphorothioate modified nucleotides are more resistant to removal by3′ 5′ exonucleases.

Whether one desires to produce an enzyme identical to native Pyrolobusfumaria DNA polymerase or a derivative or homologue of that enzyme, theproduction of a recombinant form of the polymerase typically involvesthe construction of an expression vector, the transformation of a hostcell with the vector, and culture of the transformed host cell underconditions such that expression will occur. To construct the expressionvector, a DNA is obtained that encodes the mature (used here to includeall muteins) enzyme or a fusion of the polymerase to an additionalsequence that does not destroy activity or to an additional sequencecleavable under controlled conditions (such as treatment with peptidase)to give an active protein. The coding sequence is then placed inoperable linkage with suitable control sequences in an expressionvector. The vector can be designed to replicate autonomously in the hostcell or to integrate into the chromosomal DNA of the host cell. Thevector is used to transform a suitable host, and the transformed host iscultured under conditions suitable for expression of recombinantpolymerase. The recombinant polymerase is isolated from the medium orfrom the cells; recovery and purification of the protein may not benecessary in some instances, where some impurities may be tolerated.

DEFINITIONS

As used herein, the term “DNA polymerase” encompasses enzymes havinghydrolase activity, for example, enzymes capable of use to amplify atemplate sequence during PCR amplification procedures.

The phrases “nucleic acid” or “nucleic acid sequence” as used hereinrefer to an oligonucleotide, nucleotide, polynucleotide, or to afragment of any of these, to DNA or RNA of genomic or synthetic originwhich may be single-stranded or double-stranded and may represent asense or antisense strand, to peptide nucleic acid (PNA), or to anyDNA-like or RNA-like material, natural or synthetic in origin.

A “coding sequence” or a “nucleotide sequence encoding” a particularpolypeptide or protein, is a nucleic acid sequence which is transcribedand translated into a polypeptide or protein when placed under thecontrol of appropriate regulatory sequences.

The term “gene” means the segment of DNA involved in producing apolypeptide chain; it includes regions preceding and following thecoding region (leader and trailer) as well as, where applicable,intervening sequences (introns) between individual coding segments(exons).

“Amino acid” or “amino acid sequence” as used herein refer to anoligopeptide, peptide, polypeptide, or protein sequence, or to afragment, portion, or subunit of any of these, and to naturallyoccurring or synthetic molecules.

The term “polypeptide” as used herein, refers to amino acids joined toeach other by peptide bonds or modified peptide bonds, i.e., peptideisosteres, and may contain modified amino acids other than the 20gene-encoded amino acids. The polypeptides may be modified by eithernatural processes, such as post-translational processing, or by chemicalmodification techniques which are well known in the art. Modificationscan occur anywhere in the polypeptide, including the peptide backbone,the amino acid side-chains and the amino or carboxyl termini. It will beappreciated that the same type of modification may be present in thesame or varying degrees at several sites in a given polypeptide. Also agiven polypeptide may have many types of modifications. Modificationsinclude acetylation, acylation, ADP-ribosylation, amidation, covalentattachment of flavin, covalent attachment of a heme moiety, covalentattachment of a nucleotide or nucleotide derivative, covalent attachmentof a lipid or lipid derivative, covalent attachment of aphosphytidylinositol, cross-linking cyclization, disulfide bondformation, demethylation, formation of covalent cross-links, formationof cysteine, formation of pyroglutamate, formylation,gamma-carboxylation, glycosylation, GPI anchor formation, hydroxylation,iodination, methylation, myristolyation, oxidation, pergylation,proteolytic processing, phosphorylation, prenylation, racemization,selenoylation, sulfation, and transfer-RNA mediated addition of aminoacids to protein such as arginylation. (See Proteins—Structure andMolecular Properties 2^(nd) Ed., T. E. Creighton, W.H. Freeman andCompany, New York (1993); Posttranslational Covalent Modification ofProteins, B.C. Johnson, Ed., Academic Press, New York, pp. 1-12 (1983)).

As used herein, the term “isolated” means that the material is removedfrom its original environment (e.g., the natural environment if it isnaturally occurring). For example, a naturally-occurring polynucleotideor polypeptide present in a living animal is not isolated, but the samepolynucleotide or polypeptide, separated from some or all of thecoexisting materials in the natural system, is isolated. Suchpolynucleotides could be part of a vector and/or such polynucleotides orpolypeptides could be part of a composition, and still be isolated inthat such vector or composition is not part of its natural environment.

As used herein, the term “purified” does not require absolute purity;rather, it is intended as a relative definition. Individual nucleicacids obtained from a library have been conventionally purified toelectrophoretic homogeneity. The sequences obtained from these clonescould not be obtained directly either from the library or from totalhuman DNA. The purified nucleic acids of the invention have beenpurified from the remainder of the genomic DNA in the organism by atleast 10⁴-10⁶ fold. However, the term “purified” also includes nucleicacids which have been purified from the remainder of the genomic DNA orfrom other sequences in a library or other environment by at least oneorder of magnitude, typically two or three orders, and more typicallyfour or five orders of magnitude.

The term “primer” as used herein refers to an oligonucleotide, whethernatural or synthetic, which is capable of acting as a point ofinitiation of synthesis when placed under conditions in which primerextension is initiated. Synthesis of a primer extension product which iscomplementary to a nucleic acid strand is initiated in the presence ofnucleoside triphosphates and a DNA polymerase or reverse transcriptaseenzyme in an appropriate buffer at a suitable temperature. A “buffer”includes cofactors (such as divalent metal ions) and salt (to providethe appropriate ionic strength), adjusted to the desired pH. Forinvention polymerases, the buffer preferably contains about 60 mMTris-HCl, pH 10.0, 25 mM NaOAc, 2 mM Mg(OAc)₂ to provide divalentmagnesium ions, and 0.002% NP-40/Tween-20.

A primer is preferably a single-stranded oligodeoxyribonucleotide. Theappropriate length of a primer depends on the intended use of the primerbut typically ranges from 15 to 35 nucleotides. Short primer moleculesgenerally require cooler temperatures to form sufficiently stable hybridcomplexes with the template. A primer need not reflect the exactsequence of the template but must be sufficiently complementary tohybridize with a template.

The term “primer” may refer to more than one primer, particularly in thecase where there is some ambiguity in the information regarding one orboth ends of the target region to be amplified. For instance, if anucleic acid sequence is inferred from a protein sequence, a “primer” isactually a collection of primer oligonucleotides containing sequencesrepresenting all possible codon variations based on the degeneracy ofthe genetic code. One of the primers in this collection will behomologous with the end of the target sequence. Likewise, if a“conserved” region shows significant levels of polymorphism in apopulation, mixtures of primers can be prepared that will amplifyadjacent sequences.

A primer may be “substantially” complementary to a strand of specificsequence of the template. A primer must be sufficiently complementary tohybridize with a template strand for primer elongation to occur. Aprimer sequence need not reflect the exact sequence of the template. Forexample, a non-complementary nucleotide fragment may be attached to the5′ end of the primer, with the remainder of the primer sequence beingsubstantially complementary to the strand. Non-complementary bases orlonger sequences can be interspersed into the primer, provided that theprimer sequence has sufficient complementarity with the sequence of thetemplate to hybridize and thereby form a template primer complex forsynthesis of the extension product of the primer.

A primer can be labeled, if desired, by incorporating a label detectableby spectroscopic, photochemical, biochemical, immunochemical, orchemical means. For example, useful labels include ³²P, fluorescentdyes, electron-dense reagents, enzymes (as commonly used in ELISAS),biotin, or haptens and proteins for which antisera or monoclonalantibodies are available. A label can also be used to “capture” theprimer, so as to facilitate the immobilization of either the primer or aprimer extension product, such as amplified DNA, on a solid support.

The terms “thermostable polymerase” and “thermostable enzyme” as usedherein refer to an enzyme which is stable to heat and is heat resistantat extreme high temperatures for four or more hours and which catalyzescombination of the nucleotides in the proper manner to form primerextension products that are complementary to a template nucleic acidstrand. Generally, synthesis of a primer extension product begins at the3′ end of the primer and proceeds in the 5′ direction along the templatestrand, until synthesis terminates.

The thermostable enzymes of the present invention satisfy therequirements for effective use in the amplification reaction known asthe polymerase chain reaction or PCR as described in U.S. Pat. No.4,965,188 (incorporated herein by reference). The invention enzymes donot become irreversibly denatured (inactivated) when subjected to theelevated temperatures for the time necessary to effect denaturation ofdouble-stranded nucleic acids, a key step in the PCR process.Irreversible denaturation for purposes herein refers to permanent andcomplete loss of enzymatic activity. The heating conditions necessaryfor nucleic acid denaturation will depend, e.g., on the buffer saltconcentration and the composition and length of the nucleic acids beingdenatured, but typically range from about 90° C. to about 105° C. for atime depending mainly on the temperature and the nucleic acid length,typically from a few seconds up to four minutes.

Higher temperatures may be required as the buffer salt concentrationand/or GC composition of the nucleic acid is increased. The inventionenzymes do not become irreversibly denatured from exposures totemperatures of about 95° C. to 113° C. for four hours or more. Theextreme thermostability of the invention DNA polymerase enzymes providesadditional advantages over previously characterized thermostableenzymes. Prior to the present invention, efficient PCR at denaturationtemperatures as high as 113° C. had not been demonstrated. Nothermostable DNA polymerases have been described for this purpose.However, as the G/C content of a target nucleic acid increases, thetemperature necessary to denature the duplex also increases. For targetsequences that require a denaturization step of over 95° C., previousprotocols require that solvents are included in the PCR for partiallydestabilizing the duplex, thus, lowering the effective denaturizationtemperature.

Agents such as glycerol, DMSO, or formamide have been used in thismanner in PCR (Korge et al., 1992, Proc. Natl. Acad. Sci. U.S.A.89:910-914, and Wong et al., 1991, Nuc. Acids Res. 19:2251-2259,incorporated herein by reference). However, these agents, in addition todestabilizing duplex DNA, will affect primer stability, can inhibitenzyme activity, and varying concentrations of DMSO or formamidedecrease the thermoresistance (i.e., half-life) of thermophilic DNApolymerases. Accordingly, a significant number of optimizationexperiments and reaction conditions need to be evaluated when utilizingthese cosolvents. In contrast, simply raising the denaturizationtemperature to 100° to 113° C. with the invention DNA polymerases in anotherwise standard PCR can facilitate complete strand separation of PCRproduct, eliminating the need for DNA helix destabilizing agents.

The extreme hyperthermophilic polymerases disclosed herein are stable attemperatures exceeding 100° C., and even as high as 113° C. withoutsacrificing the integrity of the target DNA, as is expected with otherknown polymerases (Ekert and Kunkel, 1992, In PCR: A Practical Approach,eds. McPherson, Quirke and Taylor, Oxford University Press, pages225-244, incorporated herein by reference).

As used herein, the term “recombinant” means that the nucleic acid isadjacent to “backbone” nucleic acid to which it is not adjacent in itsnatural environment. Additionally, to be “enriched” the nucleic acidswill represent 5% or more of the number of nucleic acid inserts in apopulation of nucleic acid backbone molecules. Backbone moleculesaccording to the invention include nucleic acids such as expressionvectors, self-replicating nucleic acids, viruses, integrating nucleicacids, and other vectors or nucleic acids used to maintain or manipulatea nucleic acid insert of interest. Typically, the enriched nucleic acidsrepresent 15% or more of the number of nucleic acid inserts in thepopulation of recombinant backbone molecules. More typically, theenriched nucleic acids represent 50% or more of the number of nucleicacid inserts in the population of recombinant backbone molecules. In aone embodiment, the enriched nucleic acids represent 90% or more of thenumber of nucleic acid inserts in the population of recombinant backbonemolecules.

“Recombinant” polypeptides or proteins refer to polypeptides or proteinsproduced by recombinant DNA techniques; i.e., produced from cellstransformed by an exogenous DNA construct encoding the desiredpolypeptide or protein. “Synthetic” polypeptides or protein are thoseprepared by chemical synthesis. Solid-phase chemical peptide synthesismethods can also be used to synthesize the polypeptide or fragments ofthe invention. Such method have been known in the art since the early1960's (Merrifield, R. B., J. Am. Chem. Soc., 85:21492154-2154, 1963)(See also Stewart, J. M. and Young, J. D., Solid Phase PeptideSynthesis, 2 ed., Pierce Chemical Co., Rockford, Ill., pp. 11-12)) andhave recently been employed in commercially available laboratory peptidedesign and synthesis kits (Cambridge Research Biochemicals). Suchcommercially available laboratory kits have generally utilized theteachings of H. M. Geysen et al, Proc. Natl. Acad. Sci., USA, 81:3998(1984) and provide for synthesizing peptides upon the tips of amultitude of “rods” or “pins” all of which are connected to a singleplate. When such a system is utilized, a plate of rods or pins isinverted and inserted into a second plate of corresponding wells orreservoirs, which contain solutions for attaching or anchoring anappropriate amino acid to the pin's or rod's tips. By repeating such aprocess step, i.e., inverting and inserting the rod's and pin's tipsinto appropriate solutions, amino acids are built into desired peptides.In addition, a number of available FMOC peptide synthesis systems areavailable. For example, assembly of a polypeptide or fragment can becarried out on a solid support using an Applied Biosystems, Inc. Model431A automated peptide synthesizer. Such equipment provides ready accessto the peptides of the invention, either by direct synthesis or bysynthesis of a series of fragments that can be coupled using other knowntechniques.

A promoter sequence is “operably linked to” a coding sequence when RNApolymerase which initiates transcription at the promoter will transcribethe coding sequence into mRNA.

“Plasmids” are designated by a lower case p preceded and/or followed bycapital letters and/or numbers. The starting plasmids herein are eithercommercially available, publicly available on an unrestricted basis, orcan be constructed from available plasmids in accord with publishedprocedures. In addition, equivalent plasmids to those described hereinare known in the art and will be apparent to the ordinarily skilledartisan.

“Digestion” of DNA refers to catalytic cleavage of the DNA with arestriction enzyme that acts only at certain sequences in the DNA. Thevarious restriction enzymes used herein are commercially available andtheir reaction conditions, cofactors and other requirements were used aswould be known to the ordinarily skilled artisan. For analyticalpurposes, typically 1 μg of plasmid or DNA fragment is used with about 2units of enzyme in about 20 μl of buffer solution. For the purpose ofisolating DNA fragments for plasmid construction, typically 5 to 50 μgof DNA are digested with 20 to 250 units of enzyme in a larger volume.Appropriate buffers and substrate amounts for particular restrictionenzymes are specified by the manufacturer. Incubation times of about 1hour at 37° C. are ordinarily used, but may vary in accordance with thesupplier's instructions. After digestion the gel electrophoresis may beperformed to isolate the desired fragment.

“Oligonucleotide” refers to either a single stranded polydeoxynucleotideor two complementary polydeoxynucleotide strands which may be chemicallysynthesized. Such synthetic oligonucleotides have no 5′ phosphate andthus will not ligate to another oligonucleotide without adding aphosphate with an ATP in the presence of a kinase. A syntheticoligonucleotide will ligate to a fragment that has not beendephosphorylated.

The phrase “substantially identical” in the context of two nucleic acidsor polypeptides, refers to two or more sequences that have at least 60%,70%, 80%, and in some aspects 90-95% nucleotide or amino acid residueidentity, when compared and aligned for maximum correspondence, asmeasured using one of the known sequence comparison algorithms or byvisual inspection. Typically, the substantial identity exists over aregion of at least about 100 residues, and most commonly the sequencesare substantially identical over at least about 150-200 residues. Insome embodiments, the sequences are substantially identical over theentire length of the coding regions.

Additionally a “substantially identical” amino acid sequence is asequence that differs from a reference sequence by one or moreconservative or non-conservative amino acid substitutions, deletions, orinsertions, particularly when such a substitution occurs at a site thatis not the active site of the molecule, and provided that thepolypeptide essentially retains its functional properties. Aconservative amino acid substitution, for example, substitutes one aminoacid for another of the same class (e.g., substitution of onehydrophobic amino acid, such as isoleucin, valine, leucine, ormethionine, for another, or substitution of one polar amino acid foranother, such as substitution of arginine for lysine, glutamic acid foraspartic acid or glutamine for asparagine). One or more amino acids canbe deleted, for example, from a polymerase polypeptide, resulting inmodification of the structure of the polypeptide, without significantlyaltering its biological activity. For example, amino- orcarboxyl-terminal amino acids that are not required for polymerasebiological activity can be removed.

Polymerase polypeptide sequences of the invention, including thosemodified as above described, can be assayed for polymerase biologicalactivity by any number of methods, including polymerizing DNA (e.g., thespeed and proofreading accuracy of polymerization). For example an assayfor the proofreading accuracy of the invention polymerase can include acomparison of the sequence of a DNA polymerized by the inventionpolymerase with a known sequence for accuracy, and the like.

Polymerase polypeptides included in the invention can have the aminoacid sequence of the of polymerase shown in FIG. 1B (SEQ ID NO:2) or 70%homology with SEQ ID NO: 2 wherein the polymerase retains polymeraseactivity at extreme high temperature, such as temperatures of about 90°C. to 113° C., from about 95° C. to 113° C., from about 100° C. to 107°C., or from about 100° C. to 105° C. Preferably, the polymerase isactive at such temperatures for one or more hours, for two or more hoursand preferably for four or more hours.

“Fragments” as used herein are a portion of a naturally occurringprotein which can exist in at least two different conformations.Fragments can have the same or substantially the same amino acidsequence as the naturally occurring protein. “Substantially the same”means that an amino acid sequence is largely, but not entirely, thesame, but retains at least one functional activity of the sequence towhich it is related. In general two amino acid sequences are“substantially the same” or “substantially homologous” if they are atleast about 85% identical. Fragments which have different threedimensional structures as the naturally occurring protein are alsoincluded. An example of this, is a “pro-form” molecule, such as a lowactivity proprotein that can be modified by cleavage to produce a maturepolymerase with significantly higher activity.

“Hybridization” refers to the process by which a nucleic acid strandjoins with a complementary strand through base pairing. Hybridizationreactions can be sensitive and selective so that a particular sequenceof interest can be identified even in samples in which it is present atlow concentrations. Suitably stringent conditions can be defined by, forexample, the concentrations of salt or formamide in the prehybridizationand hybridization solutions, or by the hybridization temperature, andare well known in the art. In particular, stringency can be increased byreducing the concentration of salt, increasing the concentration offormamide, or raising the hybridization temperature.

For example, hybridization under high stringency conditions could occurin about 50% formamide at about 37° C. to 42° C. Hybridization couldoccur under reduced stringency conditions in about 35% to 25% formamideat about 30° C. to 35° C. In particular, hybridization could occur underhigh stringency conditions at 42° C. in 50% formamide, 5×SSPE, 0.3% SDS,and 200 ng/ml sheared and denatured salmon sperm DNA. Hybridizationcould occur under reduced stringency conditions as described above, butin 35% formamide at a reduced temperature of 35° C. The temperaturerange corresponding to a particular level of stringency can be furthernarrowed by calculating the purine to pyrimidine ratio of the nucleicacid of interest and adjusting the temperature accordingly. Variationson the above ranges and conditions are well known in the art.

The term “variant” refers to polynucleotides or polypeptides of theinvention modified at one or more base pairs, codons, introns, exons, oramino acid residues (respectively) yet still retain the biologicalactivity of a polymerase of the invention. Variants can be produced byany number of means included methods such as, for example, error-pronePCR, shuffling, oligonucleotide-directed mutagenesis, assembly PCR,sexual PCR mutagenesis, in vivo mutagenesis, cassette mutagenesis,recursive ensemble mutagenesis, exponential ensemble mutagenesis,site-specific mutagenesis, ligation reassembly, GSSM and any combinationthereof.

In one aspect, the present invention provides a non-stochastic methodtermed synthetic ligation reassembly (SLR), that is somewhat related tostochastic shuffling, save that the nucleic acid building blocks are notshuffled or concatenated or chimerized randomly, but rather areassembled non-stochastically.

The SLR method does not depend on the presence of a high level ofhomology between polynucleotides to be shuffled. The invention can beused to non-stochastically generate libraries (or sets) of progenymolecules comprised of over 10¹⁰⁰ different chimeras. Conceivably, SLRcan even be used to generate libraries comprised of over 10¹⁰⁰⁰different progeny chimeras.

Thus, in one aspect, the invention provides a non-stochastic method ofproducing a set of finalized chimeric nucleic acid molecules having anoverall assembly order that is chosen by design, which method iscomprised of the steps of generating by design a plurality of specificnucleic acid building blocks having serviceable mutually compatibleligatable ends, and assembling these nucleic acid building blocks, suchthat a designed overall assembly order is achieved.

The mutually compatible ligatable ends of the nucleic acid buildingblocks to be assembled are considered to be “serviceable” for this typeof ordered assembly if they enable the building blocks to be coupled inpredetermined orders. Thus, in one aspect, the overall assembly order inwhich the nucleic acid building blocks can be coupled is specified bythe design of the ligatable ends and, if more than one assembly step isto be used, then the overall assembly order in which the nucleic acidbuilding blocks can be coupled is also specified by the sequential orderof the assembly step(s). In a one embodiment of the invention, theannealed building pieces are treated with an enzyme, such as a ligase(e.g., T4 DNA ligase) to achieve covalent bonding of the buildingpieces.

In a another embodiment, the design of nucleic acid building blocks isobtained upon analysis of the sequences of a set of progenitor nucleicacid templates that serve as a basis for producing a progeny set offinalized chimeric nucleic acid molecules. These progenitor nucleic acidtemplates thus serve as a source of sequence information that aids inthe design of the nucleic acid building blocks that are to bemutagenized, i.e. chimerized or shuffled.

In one exemplification, the invention provides for the chimerization ofa family of related genes and their encoded family of relatedpolymerases. The polymerases of the present invention can be mutagenizedin accordance with the methods described herein.

Thus according to one aspect of the invention, the sequences of aplurality of progenitor nucleic acid templates (e.g., polynucleotides ofSEQ ID NO: 1) are aligned in order to select one or more demarcationpoints, which demarcation points can be located at an area of homology.The demarcation points can be used to delineate the boundaries ofnucleic acid building blocks to be generated. Thus, the demarcationpoints identified and selected in the progenitor molecules serve aspotential chimerization points in the assembly of the progeny molecules.

Typically a serviceable demarcation point is an area of homology(comprised of at least one homologous nucleotide base) shared by atleast two progenitor templates, but the demarcation point can be an areaof homology that is shared by at least half of the progenitor templates,at least two thirds of the progenitor templates, at least three fourthsof the progenitor templates, and preferably at almost all of theprogenitor templates. Even more preferably still a serviceabledemarcation point is an area of homology that is shared by all of theprogenitor templates.

In a one embodiment, the ligation reassembly process is performedexhaustively in order to generate an exhaustive library. In other words,all possible ordered combinations of the nucleic acid building blocksare represented in the set of finalized chimeric nucleic acid molecules.At the same time, the assembly order (i.e. the order of assembly of eachbuilding block in the 5′ to 3 sequence of each finalized chimericnucleic acid) in each combination is by design (or non-stochastic).Because of the non-stochastic nature of the method, the possibility ofunwanted side products is greatly reduced.

In another embodiment, the method provides that, the ligation reassemblyprocess is performed systematically, for example in order to generate asystematically compartmentalized library, with compartments that can bescreened systematically, e.g., one by one. In other words the inventionprovides that, through the selective and judicious use of specificnucleic acid building blocks, coupled with the selective and judicioususe of sequentially stepped assembly reactions, an experimental designcan be achieved where specific sets of progeny products are made in eachof several reaction vessels. This allows a systematic examination andscreening procedure to be performed. Thus, it allows a potentially verylarge number of progeny molecules to be examined systematically insmaller groups.

Because of its ability to perform chimerizations in a manner that ishighly flexible yet exhaustive and systematic as well, particularly whenthere is a low level of homology among the progenitor molecules, theinstant invention provides for the generation of a library (or set)comprised of a large number of progeny molecules. Because of thenon-stochastic nature of the instant ligation reassembly invention, theprogeny molecules generated preferably comprise a library of finalizedchimeric nucleic acid molecules having an overall assembly order that ischosen by design. In a particularly embodiment, such a generated libraryis comprised of greater than 10³ to greater than 10¹⁰⁰⁰ differentprogeny molecular species.

In one aspect, a set of finalized chimeric nucleic acid molecules,produced as described is comprised of a polynucleotide encoding apolypeptide. According to one embodiment, this polynucleotide is a gene,which may be a man-made gene. According to another embodiment, thispolynucleotide is a gene pathway, which may be a man-made gene pathway.The invention provides that one or more man-made genes generated by theinvention may be incorporated into a man-made gene pathway, such aspathway operable in a eukaryotic organism (including a plant).

In another exemplification, the synthetic nature of the step in whichthe building blocks are generated allows the design and introduction ofnucleotides (e.g., one or more nucleotides, which may be, for example,codons or introns or regulatory sequences) that can later be optionallyremoved in an in vitro process (e.g., by mutagenesis) or in an in vivoprocess (e.g., by utilizing the gene splicing ability of a hostorganism). It is appreciated that in many instances the introduction ofthese nucleotides may also be desirable for many other reasons inaddition to the potential benefit of creating a serviceable demarcationpoint.

Thus, according to another embodiment, the invention provides that anucleic acid building block can be used to introduce an intron. Thus,the invention provides that functional introns may be introduced into aman-made gene of the invention. The invention also provides thatfunctional introns may be introduced into a man-made gene pathway of theinvention. Accordingly, the invention provides for the generation of achimeric polynucleotide that is a man-made gene containing one (or more)artificially introduced intron(s).

Accordingly, the invention also provides for the generation of achimeric polynucleotide that is a man-made gene pathway containing one(or more) artificially introduced intron(s). Preferably, theartificially introduced intron(s) are functional in one or more hostcells for gene splicing much in the way that naturally-occurring intronsserve functionally in gene splicing. The invention provides a process ofproducing man-made intron-containing polynucleotides to be introducedinto host organisms for recombination and/or splicing.

A man-made genes produced using the invention can also serve as asubstrate for recombination with another nucleic acid. Likewise, aman-made gene pathway produced using the invention can also serve as asubstrate for recombination with another nucleic acid. In a preferredinstance, the recombination is facilitated by, or occurs at, areas ofhomology between the man-made intron-containing gene and a nucleic acidwith serves as a recombination partner. In a particularly preferredinstance, the recombination partner may also be a nucleic acid generatedby the invention, including a man-made gene or a man-made gene pathway.Recombination may be facilitated by or may occur at areas of homologythat exist at the one (or more) artificially introduced intron(s) in theman-made gene.

The synthetic ligation reassembly method of the invention utilizes aplurality of nucleic acid building blocks, each of which preferably hastwo ligatable ends. The two ligatable ends on each nucleic acid buildingblock may be two blunt ends (i.e. each having an overhang of zeronucleotides), or preferably one blunt end and one overhang, or morepreferably still two overhangs.

A serviceable overhang for this purpose may be a 3′ overhang or a 5′overhang. Thus, a nucleic acid building block may have a 3′ overhang oralternatively a 5′ overhang or alternatively two 3′ overhangs oralternatively two 5′ overhangs. The overall order in which the nucleicacid building blocks are assembled to form a finalized chimeric nucleicacid molecule is determined by purposeful experimental design and is notrandom.

According to one preferred embodiment, a nucleic acid building block isgenerated by chemical synthesis of two single-stranded nucleic acids(also referred to as single-stranded oligos) and contacting them so asto allow them to anneal to form a double-stranded nucleic acid buildingblock.

A double-stranded nucleic acid building block can be of variable size.The sizes of these building blocks can be small or large. Preferredsizes for building block range from 1 base pair (not including anyoverhangs) to 100,000 base pairs (not including any overhangs). Otherpreferred size ranges are also provided, which have lower limits of from1 bp to 10,000 bp (including every integer value in between), and upperlimits of from 2 bp to 100,000 bp (including every integer value inbetween).

Many methods exist by which a double-stranded nucleic acid buildingblock can be generated that is serviceable for the invention; and theseare known in the art and can be readily performed by the skilledartisan.

According to one embodiment, a double-stranded nucleic acid buildingblock is generated by first generating two single stranded nucleic acidsand allowing them to anneal to form a double-stranded nucleic acidbuilding block. The two strands of a double-stranded nucleic acidbuilding block may be complementary at every nucleotide apart from anythat form an overhang; thus containing no mismatches, apart from anyoverhang(s). According to another embodiment, the two strands of adouble-stranded nucleic acid building block are complementary at fewerthan every nucleotide apart from any that form an overhang. Thus,according to this embodiment, a double-stranded nucleic acid buildingblock can be used to introduce codon degeneracy. Preferably the codondegeneracy is introduced using the site-saturation mutagenesis describedherein, using one or more N,N,G/T or N,N,C/T cassettes or alternativelyusing one or more N,N,N cassettes.

The in vivo recombination method of the invention can be performedblindly on a pool of unknown hybrids or alleles of a specificpolynucleotide or sequence. However, it is not necessary to know theactual DNA or RNA sequence of the specific polynucleotide.

The approach of using recombination within a mixed population of genescan be useful for the generation of any useful proteins, for example,interleukin I, antibodies, tPA and growth hormone. This approach may beused to generate proteins having altered specificity or activity. Theapproach may also be useful for the generation of hybrid nucleic acidsequences, for example, promoter regions, introns, exons, enhancersequences, 31 untranslated regions or 51 untranslated regions of genes.Thus this approach may be used to generate genes having increased ratesof expression. This approach may also be useful in the study ofrepetitive DNA sequences. Finally, this approach may be useful to mutateribozymes or aptamers.

In one aspect the invention described herein is directed to the use ofrepeated cycles of reductive reassortment, recombination and selectionwhich allow for the directed molecular evolution of highly complexlinear sequences, such as DNA, RNA or proteins thorough recombination.

In vivo shuffling of molecules is useful in providing variants and canbe performed utilizing the natural property of cells to recombinemultimers. While recombination in vivo has provided the major naturalroute to molecular diversity, genetic recombination remains a relativelycomplex process that involves 1) the recognition of homologies; 2)strand cleavage, strand invasion, and metabolic steps leading to theproduction of recombinant chiasma; and finally 3) the resolution ofchiasma into discrete recombined molecules. The formation of the chiasmarequires the recognition of homologous sequences.

In another embodiment, the invention includes a method for producing ahybrid polynucleotide from at least a first polynucleotide and a secondpolynucleotide. The invention can be used to produce a hybridpolynucleotide by introducing at least a first polynucleotide and asecond polynucleotide which share at least one region of partialsequence homology into a suitable host cell. The regions of partialsequence homology promote processes which result in sequencereorganization producing a hybrid polynucleotide. The term “hybridpolynucleotide”, as used herein, is any nucleotide sequence whichresults from the method of the present invention and contains sequencefrom at least two original polynucleotide sequences. Such hybridpolynucleotides can result from intermolecular recombination eventswhich promote sequence integration between DNA molecules. In addition,such hybrid polynucleotides can result from intramolecular reductivereassortment processes which utilize repeated sequences to alter anucleotide sequence within a DNA molecule.

The invention provides a means for generating hybrid polynucleotideswhich may encode biologically active hybrid polypeptides (e.g., hybridpolymerases). In one aspect, the original polynucleotides encodebiologically active polypeptides. The method of the invention producesnew hybrid polypeptides by utilizing cellular processes which integratethe sequence of the original polynucleotides such that the resultinghybrid polynucleotide encodes a polypeptide demonstrating activitiesderived from the original biologically active polypeptides. For example,the original polynucleotides may encode a particular polymerase fromdifferent microorganisms. A polymerase encoded by a first polynucleotidefrom one organism or variant may, for example, function effectivelyunder a particular environmental condition, e.g. high salinity. Apolymerase encoded by a second polynucleotide from a different organismor variant may function effectively under a different environmentalcondition, such as extremely high temperatures. A hybrid polynucleotidecontaining sequences from the first and second original polynucleotidesmay encode an enzyme which exhibits characteristics of both enzymesencoded by the original polynucleotides. Thus, the enzyme encoded by thehybrid polynucleotide may function effectively under environmentalconditions shared by each of the enzymes encoded by the first and secondpolynucleotides, e.g., high salinity and extreme temperatures,especially polymerase activity at extreme high temperature, such as atemperature from about 95° C. to 113° C. Some modified polynucleotidesmay achieve polymerase activity at temperatures up to 150° C., which ispresently considered to be the theoretical limit at which life formscould prevent dissolution of the chemical bonds that maintain theintegrity of DNA and other essential molecules.

Enzymes encoded by the polynucleotides of the invention include, but arenot limited to, hydrolases, such as polymerases. A hybrid polypeptideresulting from the method of the invention may exhibit specializedenzyme activity not displayed in the original enzymes. For example,following recombination and/or reductive reassortment of polynucleotidesencoding polymerase activities, the resulting hybrid polypeptide encodedby a hybrid polynucleotide can be screened for specialized polymeraseactivities obtained from each of the original enzymes, i.e. whether thepolymerase has or is free of a 3′-5′ exonuclease activity, the DNAextension rate of the polymerase, the % residual activity at altered pHas compared to the wild-type polymerase, and the optimum temperature andupper temperature limit of polymerase activity. Thus, for example, thepolymerase may be screened to ascertain those chemical functionalitieswhich distinguish the hybrid polymerase from the original polymerase,for example, the upper limit of thermal stability, the duration ofthermal stability at the upper temperature limit, or the pH or saltconcentration at which the hybrid polypeptide functions. Additionaldesirable polymerase characteristics that may be screened for includeutility of the hybrid polymerase for PCR of template molecules greaterthan 20 kb in length or containing greater than 90% guanidine-cytosine(GC) content.

Sources of the original polynucleotides may be isolated from individualorganisms (“isolates”), collections of organisms that have been grown indefined media (“enrichment cultures”), or, uncultivated organisms(“environmental samples”). The use of a culture-independent approach toderive polynucleotides encoding novel bioactivities from environmentalsamples is most preferable since it allows one to access untappedresources of biodiversity.

“Environmental libraries” are generated from environmental samples andrepresent the collective genomes of naturally occurring organismsarchived in cloning vectors that can be propagated in suitableprokaryotic hosts. Because the cloned DNA is initially extracteddirectly from environmental samples, the libraries are not limited tothe small fraction of prokaryotes that can be grown in pure culture.Additionally, polymerases that can be produced in a prokaryotic host canbe readily scaled up for commercial production. A normalization of theenvironmental DNA present in these samples could allow more equalrepresentation of the DNA from all of the species present in theoriginal sample. This can dramatically increase the efficiency offinding interesting genes from minor constituents of the sample whichmay be under-represented by several orders of magnitude compared to thedominant species.

For example, gene libraries generated from one or more uncultivatedmicroorganisms are screened for an activity of interest. Potentialpathways encoding bioactive molecules of interest are first captured inprokaryotic cells in the form of gene expression libraries.Polynucleotides encoding activities of interest are isolated from suchlibraries and introduced into a host cell. The host cell is grown underconditions which promote recombination and/or reductive reassortmentcreating potentially active biomolecules with novel or enhancedactivities.

The microorganism from which the invention polynucleotide having SEQ IDNO: 1 is derived is Pyrolobus fumaria. Additional polynucleotides may beprepared from prokaryotic microorganisms, such as Eubacteria andArchaebacteria, and lower eukaryotic microorganisms such as fungi, somealgae and protozoa. Polynucleotides may be isolated from environmentalsamples, in which case the nucleic acid may be recovered withoutculturing of an organism or recovered from one or more culturedorganisms. In order to have polymerase activity in the range above 90°C. up to 150° C. (e.g., up to 113° C.), such microorganisms arepreferably hyperthermophiles that function at temperatures above 100° C.in terrestrial hot springs and deep sea thermal vents. The polymerasesproduced by hyperthermophiles may have a lower temperature at whichenzymatic activity fails. For example, Pyrolobus fumaria ceases to growat a temperature below 90° C.

Polynucleotides selected and isolated as hereinabove described areintroduced into a suitable host cell. A suitable host cell is any cellwhich is capable of promoting recombination and/or reductivereassortment. The selected polynucleotides are preferably already in avector which includes appropriate control sequences. The host cell canbe a higher eukaryotic cell, such as a mammalian cell, or a lowereukaryotic cell, such as a yeast cell, or preferably, the host cell canbe a prokaryotic cell, such as a bacterial cell. Introduction of theconstruct into the host cell can be effected by calcium phosphatetransfection, DEAE-Dextran mediated transfection, or electroporation(Davis et al., 1986).

As representative examples of appropriate hosts, there may be mentioned:bacterial cells, such as E. coli, Streptomyces, Salmonella typhimurium;fungal cells, such as yeast; insect cells such as Drosophila S2 andSpodoptera Sf9; animal cells such as CHO, COS or Bowes melanoma;adenoviruses; and plant cells. The selection of an appropriate host isdeemed to be within the scope of those skilled in the art from theteachings herein.

With particular references to various mammalian cell culture systemsthat can be employed to express recombinant protein, examples ofmammalian expression systems include the COS-7 lines of monkey kidneyfibroblasts, described in “SV40-transformed simian cells support thereplication of early SV40 mutants” (Gluzman, 1981), and other cell linescapable of expressing a compatible vector, for example, the C127, 3T3,CHO, HeLa and BHK cell lines. Mammalian expression vectors will comprisean origin of replication, a suitable promoter and enhancer, and also anynecessary ribosome binding sites, polyadenylation site, splice donor andacceptor sites, transcriptional termination sequences, and 5′ flankingnontranscribed sequences. DNA sequences derived from the SV40 splice,and polyadenylation sites may be used to provide the requirednontranscribed genetic elements.

Host cells containing the polynucleotides of interest can be cultured inconventional nutrient media modified as appropriate for activatingpromoters, selecting transformants or amplifying genes. The cultureconditions, such as temperature, pH and the like, are those previouslyused with the host cell selected for expression, and will be apparent tothe ordinarily skilled artisan. The clones which are identified ashaving the specified polymerase activity at temperatures in the rangefrom 70° C. up to about 113° C. may then be sequenced to identify thepolynucleotide sequence encoding the polymerase.

Gene cluster DNA can be isolated from different organisms and ligatedinto vectors, particularly vectors containing expression regulatorysequences which can control and regulate the production of a detectableprotein or protein-related array activity from the ligated geneclusters. Use of vectors which have an exceptionally large capacity forexogenous DNA introduction are particularly appropriate for use withsuch gene clusters and are described by way of example herein to includethe f-factor (or fertility factor) of E. coli. This f-factor of E. coliis a plasmid which affect high-frequency transfer of itself duringconjugation and is ideal to achieve and stably propagate large DNAfragments, such as gene clusters from mixed microbial samples. Aparticularly preferred embodiment is to use cloning vectors, referred toas “fosmids” or bacterial artificial chromosome (BAC) vectors. These arederived from E. coli f-factor which is able to stably integrate largesegments of genomic DNA. When integrated with DNA from a mixeduncultured environmental sample, this makes it possible to achieve largegenomic fragments in the form of a stable “environmental DNA library.”Another type of vector for use in the present invention is a cosmidvector. Cosmid vectors were originally designed to clone and propagatelarge segments of genomic DNA. Cloning into cosmid vectors is describedin detail in “Molecular Cloning: A laboratory Manual” (Sambrook et al.,1989). Once ligated into an appropriate vector, two or more vectorscontaining different polyketide synthase gene clusters can be introducedinto a suitable host cell. Regions of partial sequence homology sharedby the gene clusters will promote processes which result in sequencereorganization resulting in a hybrid gene cluster. The novel hybrid genecluster can then be screened for polymerase activities not found in theoriginal gene clusters, or altered from that found in the original geneclusters.

Therefore, in a one embodiment, the invention relates to a method forproducing a biologically active hybrid polypeptide and screening such apolypeptide for enhanced activity by:

-   -   1) introducing at least a first polynucleotide in operable        linkage and a second polynucleotide in operable linkage, said at        least first polynucleotide and second polynucleotide sharing at        least one region of partial sequence homology, into a suitable        host cell;    -   2) growing the host cell under conditions which promote sequence        reorganization resulting in a hybrid polynucleotide in operable        linkage;    -   3) expressing a hybrid polypeptide encoded by the hybrid        polynucleotide;    -   4) screening the hybrid polypeptide under conditions which        promote identification of enhanced biological activity; and    -   5) isolating the a polynucleotide encoding the hybrid        polypeptide.

Methods for screening for polymerase activities are known to those ofskill in the art and are discussed throughout the present specification.Such methods may be employed when isolating the polypeptides andpolynucleotides of the invention.

As representative examples of expression vectors which may be used theremay be mentioned viral particles, baculovirus, phage, plasmids,phagemids, cosmids, fosmids, bacterial artificial chromosomes, viral DNA(e.g., vaccinia, adenovirus, foul pox virus, pseudorabies andderivatives of SV40), P1-based artificial chromosomes, yeast plasmids,yeast artificial chromosomes, and any other vectors specific forspecific hosts of interest (such as bacillus, aspergillus and yeast).Thus, for example, the DNA may be included in any one of a variety ofexpression vectors for expressing a polypeptide. Such vectors includechromosomal, nonchromosomal and synthetic DNA sequences. Large numbersof suitable vectors are known to those of skill in the art, and arecommercially available. The following vectors are provided by way ofexample; Bacterial: pQE vectors (Qiagen), pBluescript plasmids, pNHvectors, (lambda-ZAP vectors (Stratagene); ptrc99a, pKK223-3, pDR540,pRIT2T (Pharmacia); Eukaryotic: pXT1, pSG5 (Stratagene), pSVK3, pBPV,pMSG, pSVLSV40 (Pharmacia). However, any other plasmid or other vectormay be used so long as they are replicable and viable in the host. Lowcopy number or high copy number vectors may be employed with the presentinvention.

The DNA sequence in the expression vector is operatively linked to anappropriate expression control sequence(s) (promoter) to direct RNAsynthesis. Particular named bacterial promoters include lacI, lacZ, T3,T7, gpt, lambda P_(R), P_(L) and trp. Eukaryotic promoters include CMVimmediate early, HSV thymidine kinase, early and late SV40, LTRs fromretrovirus, and mouse metallothionein-I. Selection of the appropriatevector and promoter is well within the level of ordinary skill in theart. The expression vector also contains a ribosome binding site fortranslation initiation and a transcription terminator. The vector mayalso include appropriate sequences for amplifying expression. Promoterregions can be selected from any desired gene using CAT (chloramphenicoltransferase) vectors or other vectors with selectable markers. Inaddition, the expression vectors preferably contain one or moreselectable marker genes to provide a phenotypic trait for selection oftransformed host cells such as dihydrofolate reductase or neomycinresistance for eukaryotic cell culture, or such as tetracycline orampicillin resistance in E. coli.

In vivo reassortment is focused on “inter-molecular” processescollectively referred to as “recombination” which in bacteria, isgenerally viewed as a “RecA-dependent” phenomenon. The invention canrely on recombination processes of a host cell to recombine andre-assort sequences, or the cells' ability to mediate reductiveprocesses to decrease the complexity of quasi-repeated sequences in thecell by deletion. This process of “reductive reassortment” occurs by an“intra-molecular”, RecA-independent process.

Therefore, in another aspect of the invention, novel polynucleotides canbe generated by the process of reductive reassortment. The methodinvolves the generation of constructs containing consecutive sequences(original encoding sequences), their insertion into an appropriatevector, and their subsequent introduction into an appropriate host cell.The reassortment of the individual molecular identities occurs bycombinatorial processes between the consecutive sequences in theconstruct possessing regions of homology, or between quasi-repeatedunits. The reassortment process recombines and/or reduces the complexityand extent of the repeated sequences, and results in the production ofnovel molecular species. Various treatments may be applied to enhancethe rate of reassortment. These could include treatment withultra-violet light, or DNA damaging chemicals, and/or the use of hostcell lines displaying enhanced levels of “genetic instability”. Thus thereassortment process may involve homologous recombination or the naturalproperty of quasi-repeated sequences to direct their own evolution.

Repeated or “quasi-repeated” sequences play a role in geneticinstability. In the present invention, “quasi-repeats” are repeats thatare not restricted to their original unit structure. Quasi-repeatedunits can be presented as an array of sequences in a construct;consecutive units of similar sequences. Once ligated, the junctionsbetween the consecutive sequences become essentially invisible and thequasi-repetitive nature of the resulting construct is now continuous atthe molecular level. The deletion process the cell performs to reducethe complexity of the resulting construct operates between thequasi-repeated sequences. The quasi-repeated units provide a practicallylimitless repertoire of templates upon which slippage events can occur.The constructs containing the quasi-repeats thus effectively providesufficient molecular elasticity that deletion (and potentiallyinsertion) events can occur virtually anywhere within thequasi-repetitive units.

When the quasi-repeated sequences are all ligated in the sameorientation, for instance head to tail or vice versa, the cell cannotdistinguish individual units. Consequently, the reductive process canoccur throughout the sequences. In contrast, when for example, the unitsare presented head to head, rather than head to tail, the inversiondelineates the endpoints of the adjacent unit so that deletion formationwill favor the loss of discrete units. Thus, it is preferable with thepresent method that the sequences are in the same orientation. Randomorientation of quasi-repeated sequences will result in the loss ofreassortment efficiency, while consistent orientation of the sequenceswill offer the highest efficiency. However, while having fewer of thecontiguous sequences in the same orientation decreases the efficiency,it may still provide sufficient elasticity for the effective recovery ofnovel molecules. Constructs can be made with the quasi-repeatedsequences in the same orientation to allow higher efficiency.

Sequences can be assembled in a head to tail orientation using any of avariety of methods, including the following:

-   -   a) Primers that include a poly-A head and poly-T tail which when        made single-stranded would provide orientation can be utilized.        This is accomplished by having the first few bases of the        primers made from RNA and hence easily removed RNAseH.    -   b) Primers that include unique restriction cleavage sites can be        utilized. Multiple sites, a battery of unique sequences, and        repeated synthesis and ligation steps would be required.    -   c) The inner few bases of the primer could be thiolated and an        exonuclease used to produce properly tailed molecules.

The recovery of the re-assorted sequences relies on the identificationof cloning vectors with a reduced RI. The re-assorted encoding sequencescan then be recovered by amplification. The products are re-cloned andexpressed. The recovery of cloning vectors with reduced RI can beeffected by:

-   1) The use of vectors only stably maintained when the construct is    reduced in complexity.-   2) The physical recovery of shortened vectors by physical    procedures. In this case, the cloning vector would be recovered    using standard plasmid isolation procedures and size fractionated on    either an agarose gel, or column with a low molecular weight cut off    utilizing standard procedures.-   3) The recovery of vectors containing interrupted genes which can be    selected when insert size decreases.-   4) The use of direct selection techniques with an expression vector    and the appropriate selection.

Encoding sequences (for example, genes) from related organisms maydemonstrate a high degree of homology and encode quite diverse proteinproducts. These types of sequences are particularly useful in thepresent invention as quasi-repeats. However, while the examplesillustrated below demonstrate the reassortment of nearly identicaloriginal encoding sequences (quasi-repeats), this process is not limitedto such nearly identical repeats.

The following example demonstrates a method of the invention. Encodingnucleic acid sequences (quasi-repeats) derived from three (3) uniquespecies are described. Each sequence encodes a protein with a distinctset of properties. Each of the sequences differs by a single or a fewbase pairs at a unique position in the sequence. The quasi-repeatedsequences are separately or collectively amplified and ligated intorandom assemblies such that all possible permutations and combinationsare available in the population of ligated molecules. The number ofquasi-repeat units can be controlled by the assembly conditions. Theaverage number of quasi-repeated units in a construct is defined as therepetitive index (RI).

Once formed, the constructs may, or may not be size fractionated on anagarose gel according to published protocols, inserted into a cloningvector, and transfected into an appropriate host cell. The cells arethen propagated and “reductive reassortment” is effected. The rate ofthe reductive reassortment process may be stimulated by the introductionof DNA damage if desired. Whether the reduction in RI is mediated bydeletion formation between repeated sequences by an “intra-molecular”mechanism, or mediated by recombination-like events through“inter-molecular” mechanisms is immaterial. The end result is areassortment of the molecules into all possible combinations.

Optionally, the method comprises the additional step of screening thelibrary members of the shuffled pool to identify individual shuffledlibrary members having the ability to bind or otherwise interact, orcatalyze a particular amplification reaction (e.g., such as catalyticdomain of a DNA polymerase) with a predetermined macromolecule, such asfor example a proteinaceous receptor, an oligosaccharide, viron, orother predetermined compound or structure.

The polypeptides that are identified from such libraries can be used fortherapeutic, diagnostic, research and related purposes (e.g., catalysts,solutes for increasing osmolarity of an aqueous solution, and the like),and/or can be subjected to one or more additional cycles of shufflingand/or selection.

In another aspect, it is envisioned that prior to or duringrecombination or reassortment, polynucleotides generated by the methodof the invention can be subjected to agents or processes which promotethe introduction of mutations into the original polynucleotides. Theintroduction of such mutations would increase the diversity of resultinghybrid polynucleotides and polypeptides encoded therefrom. The agents orprocesses which promote mutagenesis can include, but are not limited to:(+)-CC-1065, or a synthetic analog such as (+)-CC-1065-(N3-Adenine, seeSun and Hurley, 1992); an N-acelylated or deacetylated4′-fluro-4-aminobiphenyl adduct capable of inhibiting DNA synthesis(see, for example, van de Poll et al., 1992); or a N-acetylated ordeacetylated 4-aminobiphenyl adduct capable of inhibiting DNA synthesis(see also, van de Poll et al., 1992, pp. 751-758); trivalent chromium, atrivalent chromium salt, a polycyclic aromatic hydrocarbon (“PAH”) DNAadduct capable of inhibiting DNA replication, such as7-bromomethyl-benz[a]anthracene (“BMA”),tris(2,3-dibromopropyl)phosphate (“Tris-BP”),1,2-dibromo-3-chloropropane (“DBCP”), 2-bromoacrolein (2BA),benzo[a]pyrene-7,8-dihydrodiol-9-10-epoxide (“BPDE”), a platinum(II)halogen salt, N-hydroxy-2-amino-3-methylimidazo[4,5-f]-quinoline(“N-hydroxy-IQ”), andN-hydroxy-2-amino-1-methyl-6-phenylimidazo[4,5-f]-pyridine(“N-hydroxy-PhIP”). Especially preferred means for slowing or haltingPCR amplification consist of UV light (+)-CC-1065 and(+)-CC-1065-(N3-Adenine). Particularly encompassed means are DNA adductsor polynucleotides comprising the DNA adducts from the polynucleotidesor polynucleotides pool, which can be released or removed by a processincluding heating the solution comprising the polynucleotides prior tofurther processing.

In another aspect the invention is directed to a method of producingrecombinant proteins having biological activity by treating a samplecomprising double-stranded template polynucleotides encoding a wild-typeprotein under conditions according to the invention which provide forthe production of hybrid or re-assorted polynucleotides.

The invention also provides for the use of proprietary codon primers(containing a degenerate N,N,N sequence) to introduce point mutationsinto a polynucleotide, so as to generate a set of progeny polypeptidesin which a full range of single amino acid substitutions is representedat each amino acid position (gene site saturated mutagenesis (GSSM)).The oligos used are comprised contiguously of a first homologoussequence, a degenerate N,N,N sequence, and preferably but notnecessarily a second homologous sequence. The downstream progenytranslational products from the use of such oligos include all possibleamino acid changes at each amino acid site along the polypeptide,because the degeneracy of the N,N,N sequence includes codons for all 20amino acids.

In one aspect, one such degenerate oligo (comprised of one degenerateN,N,N cassette) is used for subjecting each original codon in a parentalpolynucleotide template to a full range of codon substitutions. Inanother aspect, at least two degenerate N,N,N cassettes are used—eitherin the same oligo or not, for subjecting at least two original codons ina parental polynucleotide template to a full range of codonsubstitutions. Thus, more than one N,N,N sequence can be contained inone oligo to introduce amino acid mutations at more than one site. Thisplurality of N,N,N sequences can be directly contiguous, or separated byone or more additional nucleotide sequence(s). In another aspect, oligosserviceable for introducing additions and deletions can be used eitheralone or in combination with the codons containing an N,N,N sequence, tointroduce any combination or permutation of amino acid additions,deletions, and/or substitutions.

In a particular exemplification, it is possible to simultaneouslymutagenize two or more contiguous amino acid positions using an oligothat contains contiguous N,N,N triplets, i.e. a degenerate (N,N,N)_(n)sequence.

In another aspect, the present invention provides for the use ofdegenerate cassettes having less degeneracy than the N,N,N sequence. Forexample, it may be desirable in some instances to use (e.g. in an oligo)a degenerate triplet sequence comprised of only one N, where said N canbe in the first second or third position of the triplet. Any other basesincluding any combinations and permutations thereof can be used in theremaining two positions of the triplet. Alternatively, it may bedesirable in some instances to use (e.g., in an oligo) a degenerateN,N,N triplet sequence, N,N,G/T, or an N,N, G/IC triplet sequence.

It is appreciated, however, that the use of a degenerate triplet (suchas N,N,G/T or an N,N, G/C triplet sequence) as disclosed in the instantinvention is advantageous for several reasons. In one aspect, thisinvention provides a means to systematically and fairly easily generatethe substitution of the full range of possible amino acids (for a totalof 20 amino acids) into each and every amino acid position in apolypeptide. Thus, for a 100 amino acid polypeptide, the inventionprovides a way to systematically and fairly easily generate 2000distinct species (i.e., 20 possible amino acids per position times 100amino acid positions). It is appreciated that there is provided, throughthe use of an oligo containing a degenerate N,N,G/T or an N,N, G/Ctriplet sequence, 32 individual sequences that code for 20 possibleamino acids. Thus, in a reaction vessel in which a parentalpolynucleotide sequence is subjected to saturation mutagenesis using onesuch oligo, there are generated 32 distinct progeny polynucleotidesencoding 20 distinct polypeptides. In contrast, the use of anondegenerate oligo in site-directed mutagenesis leads to only oneprogeny polypeptide product per reaction vessel.

This invention also provides for the use of nondegenerate oligos, whichcan optionally be used in combination with degenerate primers disclosed.It is appreciated that in some situations, it is advantageous to usenondegenerate oligos to generate specific point mutations in a workingpolynucleotide. This provides a means to generate specific silent pointmutations, point mutations leading to corresponding amino acid changes,and point mutations that cause the generation of stop codons and thecorresponding expression of polypeptide fragments.

Thus, in a preferred embodiment of this invention, each saturationmutagenesis reaction vessel contains polynucleotides encoding at least20 progeny polypeptide molecules such that all 20 amino acids arerepresented at the one specific amino acid position corresponding to thecodon position mutagenized in the parental polynucleotide. The 32-folddegenerate progeny polypeptides generated from each saturationmutagenesis reaction vessel can be subjected to clonal amplification(e.g., cloned into a suitable E. coli host using an expression vector)and subjected to expression screening. When an individual progenypolypeptide is identified by screening to display a favorable change inproperty (when compared to the parental polypeptide), it can besequenced to identify the correspondingly favorable amino acidsubstitution contained therein.

It is appreciated that upon mutagenizing each and every amino acidposition in a parental polypeptide using saturation mutagenesis asdisclosed herein, favorable amino acid changes may be identified at morethan one amino acid position. One or more new progeny molecules can begenerated that contain a combination of all or part of these favorableamino acid substitutions. For example, if 2 specific favorable aminoacid changes are identified in each of 3 amino acid positions in apolypeptide, the permutations include 3 possibilities at each position(no change from the original amino acid, and each of two favorablechanges) and 3 positions. Thus, there are 3×3×3 or 27 totalpossibilities, including 7 that were previously examined—6 single pointmutations (i.e., 2 at each of three positions) and no change at anyposition.

In yet another aspect, site-saturation mutagenesis can be used togetherwith shuffling, chimerization, recombination and other mutagenizingprocesses, along with screening. This invention provides for the use ofany mutagenizing process(es), including saturation mutagenesis, in aniterative manner. In one exemplification, the iterative use of anymutagenizing process(es) is used in combination with screening.

Thus, in a non-limiting exemplification, this invention provides for theuse of saturation mutagenesis in combination with additionalmutagenization processes, such as process where two or more relatedpolynucleotides are introduced into a suitable host cell such that ahybrid polynucleotide is generated by recombination and reductivereassortment.

In addition to performing mutagenesis along the entire sequence of agene, the instant invention provides that mutagenesis can be use toreplace each of any number of bases in a polynucleotide sequence,wherein the number of bases to be mutagenized is preferably everyinteger from 15 to 100,000. Thus, instead of mutagenizing every positionalong a molecule, one can subject every or a discrete number of bases(preferably a subset totaling from 15 to 100,000) to mutagenesis.Preferably, a separate nucleotide is used for mutagenizing each positionor group of positions along a polynucleotide sequence. A group of 3positions to be mutagenized may be a codon. The mutations are preferablyintroduced using a mutagenic primer, containing a heterologous cassette,also referred to as a mutagenic cassette. Preferred cassettes can havefrom 1 to 500 bases. Each nucleotide position in such heterologouscassettes be N, A, C, G, T, A/C, A/G, A/T, C/G, C/T, G/T, C/G/T, A/G/T,A/C/T, A/C/G, or E, where E is any base that is not A, C, G, or T (E canbe referred to as a designer oligo).

In a general sense, saturation mutagenesis is comprised of mutagenizinga complete set of mutagenic cassettes (wherein each cassette ispreferably about 1-500 bases in length) in defined polynucleotidesequence to be mutagenized (wherein the sequence to be mutagenized ispreferably from about 15 to 100,000 bases in length). Thus, a group ofmutations (ranging from 1 to 100 mutations) is introduced into eachcassette to be mutagenized. A grouping of mutations to be introducedinto one cassette can be different or the same from a second grouping ofmutations to be introduced into a second cassette during the applicationof one round of saturation mutagenesis. Such groupings are exemplifiedby deletions, additions, groupings of particular codons, and groupingsof particular nucleotide cassettes.

Defined sequences to be mutagenized include a whole gene, pathway, cDNA,an entire open reading frame (ORF), and entire promoter, enhancer,repressor/transactivator, origin of replication, intron, operator, orany polynucleotide functional group. Generally, a “defined sequences”for this purpose may be any polynucleotide that a 15 base-polynucleotidesequence, and polynucleotide sequences of lengths between 15 bases and15,000 bases (this invention specifically names every integer inbetween). Considerations in choosing groupings of codons include typesof amino acids encoded by a degenerate mutagenic cassette.

In a particularly preferred exemplification a grouping of mutations thatcan be introduced into a mutagenic cassette, this invention specificallyprovides for degenerate codon substitutions (using degenerate oligos)that code for 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17,18, 19, and 20 amino acids at each position, and a library ofpolypeptides encoded thereby.

One aspect of the invention is an isolated nucleic acid comprising oneof the sequences of SEQ ID NO: 1, and sequences substantially identicalthereto, the sequences complementary thereto, or a fragment comprisingat least 10, 15, 20, 25, 30, 35, 40, 50, 75, 100, 150, 200, 300, 400, or500 consecutive bases of one of the sequences of a Group A nucleic acidsequence (or the sequences complementary thereto). The isolated, nucleicacids may comprise DNA, including cDNA, genomic DNA, and synthetic DNA.The DNA may be double-stranded or single-stranded, and if singlestranded may be the coding strand or non-coding (anti-sense) strand.Alternatively, the isolated nucleic acids may comprise RNA.

As discussed in more detail below, the isolated nucleic acids of one ofthe SEQ ID NO: 1, and sequences substantially identical thereto, may beused to prepare one of the polypeptides of a Group B amino acidsequence, and sequences substantially identical thereto, or fragmentscomprising at least 5, 10, 15, 20, 25, 30, 35, 40, 50, 75, 100, or 150consecutive amino acids of one of the polypeptides of SEQ ID NO: 2, andsequences substantially identical thereto.

Accordingly, another aspect of the invention is an isolated nucleic acidwhich encodes one of the polypeptides of SEQ ID NO: 2, and sequencessubstantially identical thereto, or fragments comprising at least 5, 10,15, 20, 25, 30, 35, 40, 50, 75, 100, or 150 consecutive amino acids ofone of the polypeptides of the SEQ ID NO: 2. The coding sequences ofthese nucleic acids may be identical to one of the coding sequences ofone of the nucleic acids of SEQ ID NO: 1, or a fragment thereof or maybe different coding sequences which encode one of the polypeptides ofSEQ ID NO: 2, sequences substantially identical thereto, and fragmentshaving at least 5, 10, 15, 20, 25, 30, 35, 40, 50, 75, 100, or 150consecutive amino acids of one of the polypeptides of SEQ ID NO: 2, as aresult of the redundancy or degeneracy of the genetic code. The geneticcode is well known to those of skill in the art and can be obtained, forexample, on page 214 of B. Lewin, Genes VI, Oxford University Press,1997, the disclosure of which is incorporated herein by reference.

The isolated nucleic acid which encodes one of the polypeptides of SEQID NO: 2, and sequences substantially identical thereto, may include,but is not limited to: only the coding sequence of one of SEQ ID NO: 1,and sequences substantially identical thereto, and additional codingsequences, such as leader sequences or proprotein sequences andnon-coding sequences, such as introns or non-coding sequences 5′ and/or3′ of the coding sequence. Thus, as used herein, the term“polynucleotide encoding a polypeptide” encompasses a polynucleotidewhich includes only coding sequence for the polypeptide as well as apolynucleotide which includes additional coding and/or non-codingsequence.

Alternatively, the nucleic acid sequences of SEQ ID NO: 1, and sequencessubstantially identical thereto, may be mutagenized using conventionaltechniques, such as site directed mutagenesis, or other techniquesfamiliar to those skilled in the art, to introduce silent changes intothe polynucleotides of SEQ ID NO: 1, and sequences substantiallyidentical thereto. As used herein, “silent changes” include, forexample, changes which do not alter the amino acid sequence encoded bythe polynucleotide. Such changes may be desirable in order to increasethe level of the polypeptide produced by host cells containing a vectorencoding the polypeptide by introducing codons or codon pairs whichoccur frequently in the host organism.

The invention also relates to polynucleotides which have nucleotidechanges which result in amino acid substitutions, additions, deletions,fusions and truncations in the polypeptides of SEQ ID NO: 2, andsequences substantially identical thereto. Such nucleotide changes maybe introduced using techniques such as site directed mutagenesis, randomchemical mutagenesis, exonuclease III deletion, and other recombinantDNA techniques. Alternatively, such nucleotide changes may be naturallyoccurring allelic variants which are isolated by identifying nucleicacids which specifically hybridize to probes comprising at least 10, 15,20, 25, 30, 35, 40, 50, 75, 100, 150, 200, 300, 400, or 500 consecutivebases of one of the sequences of SEQ ID NO: 1, and sequencessubstantially identical thereto (or the sequences complementary thereto)under conditions of high, moderate, or low stringency as providedherein.

The isolated nucleic acids of SEQ ID NO: 1, and sequences substantiallyidentical thereto, the sequences complementary thereto, or a fragmentcomprising at least 10, 15, 20, 25, 30, 35, 40, 50, 75, 100, 150, 200,300, 400, or 500 consecutive bases of one of the sequences of SEQ ID NO:1, and sequences substantially identical thereto, or the sequencescomplementary thereto may also be used as probes to determine whether abiological sample, such as a soil sample, contains an organism having anucleic acid sequence of the invention or an organism from which thenucleic acid was obtained. In such procedures, a biological samplepotentially harboring the organism from which the nucleic acid wasisolated is obtained and nucleic acids are obtained from the sample. Thenucleic acids are contacted with the probe under conditions which permitthe probe to specifically hybridize to any complementary sequences fromwhich are present therein.

Where necessary, conditions which permit the probe to specificallyhybridize to complementary sequences may be determined by placing theprobe in contact with complementary sequences from samples known tocontain the complementary sequence as well as control sequences which donot contain the complementary sequence. Hybridization conditions, suchas the salt concentration of the hybridization buffer, the formamideconcentration of the hybridization buffer, or the hybridizationtemperature, may be varied to identify conditions which allow the probeto hybridize specifically to complementary nucleic acids.

If the sample contains the organism from which the nucleic acid wasisolated, specific hybridization of the probe is then detected.Hybridization may be detected by labeling the probe with a detectableagent such as a radioactive isotope, a fluorescent dye or an enzymecapable of catalyzing the formation of a detectable product.

Many methods for using the labeled probes to detect the presence ofcomplementary nucleic acids in a sample are familiar to those skilled inthe art. These include Southern Blots, Northern Blots, colonyhybridization procedures, and dot blots. Protocols for each of theseprocedures are provided in Ausubel et al. Current Protocols in MolecularBiology, John Wiley 503 Sons, Inc. 1997 and Sambrook et al., MolecularCloning: A Laboratory Manual 2d Ed., Cold Spring Harbor LaboratoryPress, 1989, the entire disclosures of which are incorporated herein byreference.

Alternatively, more than one probe (at least one of which is capable ofspecifically hybridizing to any complementary sequences which arepresent in the nucleic acid sample), may be used in an amplificationreaction to determine whether the sample contains an organism containinga nucleic acid sequence of the invention (e.g., an organism from whichthe nucleic acid was isolated). Typically, the probes compriseoligonucleotides. In one embodiment, the amplification reaction maycomprise a PCR reaction. PCR protocols are described in Ausubel andSambrook, supra. Alternatively, the amplification may comprise a ligasechain reaction, 3SR, or strand displacement reaction. (See Barany, F.,“The Ligase Chain Reaction in a PCR World”, PCR Methods and Applications1:5-16, 1991; E. Fahy et al., “Self-sustained Sequence Replication(3SR): An Isothermal Transcription-based Amplification SystemAlternative to PCR”, PCR Methods and Applications 1:25-33, 1991; andWalker G. T. et al., “Strand Displacement Amplification—an Isothermal invitro DNA Amplification Technique”, Nucleic Acid Research 20:1691-1696,1992, the disclosures of which are incorporated herein by reference intheir entireties). In such procedures, the nucleic acids in the sampleare contacted with the probes, the amplification reaction is performed,and any resulting amplification product is detected. The amplificationproduct may be detected by performing gel electrophoresis on thereaction products and staining the gel with an interculator such asethidium bromide. Alternatively, one or more of the probes may belabeled with a radioactive isotope and the presence of a radioactiveamplification product may be detected by autoradiography after gelelectrophoresis.

Probes derived from sequences near the ends of the sequences of SEQ IDNO: 1, and sequences substantially identical thereto, may also be usedin chromosome walking procedures to identify clones containing genomicsequences located adjacent to the sequences of SEQ ID NO: 1, andsequences substantially identical thereto. Such methods allow theisolation of genes which encode additional proteins from the hostorganism.

The isolated nucleic acids of SEQ ID NO: 1, and sequences substantiallyidentical thereto, the sequences complementary thereto, or a fragmentcomprising at least 10, 15, 20, 25, 30, 35, 40, 50, 75, 100, 150, 200,300, 400, or 500 consecutive bases of one of the sequences of SEQ ID NO:1, and sequences substantially identical thereto, or the sequencescomplementary thereto may be used as probes to identify and isolaterelated nucleic acids. In some embodiments, the related nucleic acidsmay be cDNAs or genomic DNAs from organisms other than the one fromwhich the nucleic acid was isolated. For example, the other organismsmay be related organisms. In such procedures, a nucleic acid sample iscontacted with the probe under conditions which permit the probe tospecifically hybridize to related sequences. Hybridization of the probeto nucleic acids from the related organism is then detected using any ofthe methods described above.

In nucleic acid hybridization reactions, the conditions used to achievea particular level of stringency will vary, depending on the nature ofthe nucleic acids being hybridized. For example, the length, degree ofcomplementarity, nucleotide sequence composition (e.g., GC v. ATcontent), and nucleic acid type (e.g., RNA v. DNA) of the hybridizingregions of the nucleic acids can be considered in selectinghybridization conditions. An additional consideration is whether one ofthe nucleic acids is immobilized, for example, on a filter.

Hybridization may be carried out under conditions of low stringency,moderate stringency or high stringency. As an example of nucleic acidhybridization, a polymer membrane containing immobilized denaturednucleic acids is first prehybridized for 30 minutes at 45° C. in asolution consisting of 0.9 M NaCl, 50 mM NaH₂PO₄, pH 7.0, 5.0 mMNa₂EDTA, 0.5% SDS, 10×Denhardt's, and 0.5 mg/ml polyriboadenylic acid.Approximately 2×10⁷ cpm (specific activity 4-9×10⁸ cpm/ug) of ³²Pend-labeled oligonucleotide probe are then added to the solution. After12-16 hours of incubation, the membrane is washed for 30 minutes at roomtemperature in 1×SET (150 mM NaCl, 20 mM Tris hydrochloride, pH 7.8, 1mM Na₂EDTA) containing 0.5% SDS, followed by a 30 minute wash in fresh1×SET at Tm-10° C. for the oligonucleotide probe. The membrane is thenexposed to auto-radiographic film for detection of hybridizationsignals.

By varying the stringency of the hybridization conditions used toidentify nucleic acids, such as cDNAs or genomic DNAs, which hybridizeto the detectable probe, nucleic acids having different levels ofhomology to the probe can be identified and isolated. Stringency may bevaried by conducting the hybridization at varying temperatures below themelting temperatures of the probes. The melting temperature, T_(m), isthe temperature (under defined ionic strength and pH) at which 50% ofthe target sequence hybridizes to a perfectly complementary probe. Verystringent conditions are selected to be equal to or about 5° C. lowerthan the T_(m) for a particular probe. The melting temperature of theprobe may be calculated using the following formulas:

For probes between 14 and 70 nucleotides in length the meltingtemperature (T_(m)) is calculated using the formula: T_(m)=81.5+16.6(log[Na+])+0.41(fraction G+C)−(600/N) where N is the length of the probe.

If the hybridization is carried out in a solution containing formamide,the melting temperature may be calculated using the equation:T_(m)=81.5+16.6(log [Na+])+0.41(fraction G+C)−(0.63% formamide)-(600/N)where N is the length of the probe.

Prehybridization may be carried out in 6×SSC, 5×Denhardt's reagent, 0.5%SDS, 100 μg denatured fragmented salmon sperm DNA or 6×SSC, 5×Denhardt'sreagent, 0.5% SDS, 100 μg denatured fragmented salmon sperm DNA, 50%formamide. The formulas for SSC and Denhardt's solutions are listed inSambrook et al., supra.

Hybridization is conducted by adding the detectable probe to theprehybridization solutions listed above. Where the probe comprisesdouble stranded DNA, it is denatured before addition to thehybridization solution. The filter is contacted with the hybridizationsolution for a sufficient period of time to allow the probe to hybridizeto cDNAs or genomic DNAs containing sequences complementary thereto orhomologous thereto. For probes over 200 nucleotides in length, thehybridization may be carried out at 15-25° C. below the Tm. For shorterprobes, such as oligonucleotide probes, the hybridization may beconducted at 5-10° C. below the T_(m). Typically, for hybridizations in6×SSC, the hybridization is conducted at approximately 68° C. Usually,for hybridizations in 50% formamide containing solutions, thehybridization is conducted at approximately 42° C.

All of the foregoing hybridizations would be considered to be underconditions of high stringency.

Following hybridization, the filter is washed to remove anynon-specifically bound detectable probe. The stringency used to wash thefilters can also be varied depending on the nature of the nucleic acidsbeing hybridized, the length of the nucleic acids being hybridized, thedegree of complementarity, the nucleotide sequence composition (e.g., GCv. AT content), and the nucleic acid type (e.g., RNA, v. DNA). Examplesof progressively higher stringency condition washes are as follows:2×SSC, 0.1% SDS at room temperature for 15 minutes (low stringency);0.1×SSC, 0.5% SDS at room temperature for 30 minutes to 1 hour (moderatestringency); 0.1×SSC, 0.5% SDS for 15 to 30 minutes at between thehybridization temperature and 68° C. (high stringency); and 0.15M NaClfor 15 minutes at 72° C. (very high stringency). A final low stringencywash can be conducted in 0.1×SSC at room temperature. The examples aboveare merely illustrative of one set of conditions that can be used towash filters. One of skill in the art would know that there are numerousrecipes for different stringency washes. Some other examples are givenbelow.

Nucleic acids which have hybridized to the probe are identified byautoradiography or other conventional techniques.

The above procedure may be modified to identify nucleic acids havingdecreasing levels of homology to the probe sequence. For example, toobtain nucleic acids of decreasing homology to the detectable probe,less stringent conditions may be used. For example, the hybridizationtemperature may be decreased in increments of 5° C. from 68° C. to 42°C. in a hybridization buffer having a Na+ concentration of approximately1M. Following hybridization, the filter may be washed with 2×SSC, 0.5%SDS at the temperature of hybridization. These conditions are consideredto be “moderate” conditions above 50° C. and “low” conditions below 50°C. A specific example of “moderate” hybridization conditions is when theabove hybridization is conducted at 55° C. A specific example of “lowstringency” hybridization conditions is when the above hybridization isconducted at 45° C.

Alternatively, the hybridization may be carried out in buffers, such as6×SSC, containing formamide at a temperature of 42° C. In this case, theconcentration of formamide in the hybridization buffer may be reduced in5% increments from 50% to 0% to identify clones having decreasing levelsof homology to the probe. Following hybridization, the filter may bewashed with 6×SSC, 0.5% SDS at 50° C. These conditions are considered tobe “moderate” conditions above 25% formamide and “low” conditions below25% formamide. A specific example of “moderate” hybridization conditionsis when the above hybridization is conducted at 30% formamide. Aspecific example of “low stringency” hybridization conditions is whenthe above hybridization is conducted at 10% formamide.

For example, the preceding methods may be used to isolate nucleic acidshaving a sequence with at least about 97%, at least 95%, at least 90%,at least 85%, at least 80%, or at least 70% homology to a nucleic acidsequence selected from the group consisting of one of the sequences ofSEQ ID NO: 1, and sequences substantially identical thereto, orfragments comprising at least about 10, 15, 20, 25, 30, 35, 40, 50, 75,100, 150, 200, 300, 400, or 500 consecutive bases thereof, and thesequences complementary thereto. Homology may be measured using thealignment algorithm. For example, the homologous polynucleotides mayhave a coding sequence which is a naturally occurring allelic variant ofone of the coding sequences described herein. Such allelic variants mayhave a substitution, deletion or addition of one or more nucleotideswhen compared to the nucleic acids of SEQ ID NO: 1 or the sequencescomplementary thereto.

Additionally, the above procedures may be used to isolate nucleic acidswhich encode polypeptides having at least about 99%, 95%, at least 90%,at least 85%, at least 80%, or at least 70% homology to a polypeptidehaving the sequence of one of SEQ ID NO: 2, and sequences substantiallyidentical thereto, or fragments comprising at least 5, 10, 15, 20, 25,30, 35, 40, 50, 75, 100, or 150 consecutive amino acids thereof asdetermined using a sequence alignment algorithm (e.g., such as the FASTAversion 3.0t78 algorithm with the default parameters).

Another aspect of the invention is an isolated or purified polypeptidecomprising the sequence of one of SEQ ID NO: 1, and sequencessubstantially identical thereto, or fragments comprising at least about5, 10, 15, 20, 25, 30, 35, 40, 50, 75, 100, or 150 consecutive aminoacids thereof. As discussed above, such polypeptides may be obtained byinserting a nucleic acid encoding the polypeptide into a vector suchthat the coding sequence is operably linked to a sequence capable ofdriving the expression of the encoded polypeptide in a suitable hostcell. For example, the expression vector may comprise a promoter, aribosome binding site for translation initiation and a transcriptionterminator. The vector may also include appropriate sequences foramplifying expression.

Promoters suitable for expressing the polypeptide or fragment thereof inbacteria include the E. coli lac or trp promoters, the lacI promoter,the lacZ promoter, the T3 promoter, the T7 promoter, the gpt promoter,the lambda P_(R) promoter, the lambda P_(L) promoter, promoters fromoperons encoding glycolytic enzymes such as 3-phosphoglycerate kinase(PGK), and the acid phosphatase promoter. Fungal promoters include the Vfactor promoter. Eukaryotic promoters include the CMV immediate earlypromoter, the HSV thymidine kinase promoter, heat shock promoters, theearly and late SV40 promoter, LTRs from retroviruses, and the mousemetallothionein-I promoter. Other promoters known to control expressionof genes in prokaryotic or eukaryotic cells or their viruses may also beused.

Mammalian expression vectors may also comprise an origin of replication,any necessary ribosome binding sites, a polyadenylation site, splicedonor and acceptor sites, transcriptional termination sequences, and 5′flanking nontranscribed sequences. In some embodiments, DNA sequencesderived from the SV40 splice and polyadenylation sites may be used toprovide the required nontranscribed genetic elements.

Vectors for expressing the polypeptide or fragment thereof in eukaryoticcells may also contain enhancers to increase expression levels.Enhancers are cis-acting elements of DNA, usually from about 10 to about300 bp in length that act on a promoter to increase its transcription.Examples include the SV40 enhancer on the late side of the replicationorigin bp 100 to 270, the cytomegalovirus early promoter enhancer, thepolyoma enhancer on the late side of the replication origin, and theadenovirus enhancers.

In addition, the expression vectors typically contain one or moreselectable marker genes to permit selection of host cells containing thevector. Such selectable markers include genes encoding dihydrofolatereductase or genes conferring neomycin resistance for eukaryotic cellculture, genes conferring tetracycline or ampicillin resistance in E.coli, and the S. cerevisiae TRP1 gene.

In some embodiments, the nucleic acid encoding one of the polypeptidesof SEQ ID NO: 2, and sequences substantially identical thereto, orfragments comprising at least about 5, 10, 15, 20, 25, 30, 35, 40, 50,75, 100, or 150 consecutive amino acids thereof is assembled inappropriate phase with a leader sequence capable of directing secretionof the translated polypeptide or fragment thereof. Optionally, thenucleic acid can encode a fusion polypeptide in which one of thepolypeptides of SEQ ID NO: 2, and sequences substantially identicalthereto, or fragments comprising at least 5, 10, 15, 20, 25, 30, 35, 40,50, 75, 100, or 150 consecutive amino acids thereof is fused toheterologous peptides or polypeptides, such as N-terminal identificationpeptides which impart desired characteristics, such as increasedstability or simplified purification.

The appropriate DNA sequence may be inserted into the vector by avariety of procedures. In general, the DNA sequence is ligated to thedesired position in the vector following digestion of the insert and thevector with appropriate restriction endonucleases. Alternatively, bluntends in both the insert and the vector may be ligated. A variety ofcloning techniques are disclosed in Ausubel et al. Current Protocols inMolecular Biology, John Wiley 503 Sons, Inc. 1997 and Sambrook et al.,Molecular Cloning: A Laboratory Manual 2d Ed., Cold Spring HarborLaboratory Press, 1989, the entire disclosures of which are incorporatedherein by reference. Such procedures and others are deemed to be withinthe scope of those skilled in the art.

The vector may be, for example, in the form of a plasmid, a viralparticle, or a phage. Other vectors include chromosomal, nonchromosomaland synthetic DNA sequences, derivatives of SV40; bacterial plasmids,phage DNA, baculovirus, yeast plasmids, vectors derived fromcombinations of plasmids and phage DNA, viral DNA such as vaccinia,adenovirus, fowl pox virus, and pseudorabies. A variety of cloning andexpression vectors for use with prokaryotic and eukaryotic hosts aredescribed by Sambrook, et al., Molecular Cloning: A Laboratory Manual,Second Edition, Cold Spring Harbor, N.Y., (1989), the disclosure ofwhich is hereby incorporated by reference.

Particular bacterial vectors which may be used include the commerciallyavailable plasmids comprising genetic elements of the well known cloningvector pBR322 (ATCC 37017), pKK223-3 (Pharmacia Fine Chemicals, Uppsala,Sweden), GEM1 (Promega Biotec, Madison, Wis., USA) pQE70, pQE60, pQE-9(Qiagen), pD10, psiX174 pBluescript II KS, pNH8A, pNH16a, pNH18A, pNH46A(Stratagene), ptrc99a, pKK223-3, pKK233-3, pDR540, pRIT5 (Pharmacia),pKK232-8 and pCM7. Particular eukaryotic vectors include pSV2CAT, pOG44,pXT1, pSG (Stratagene) pSVK3, pBPV, pMSG, and pSVL (Pharmacia). However,any other vector may be used as long as it is replicable and viable inthe host cell.

The host cell may be any of the host cells familiar to those skilled inthe art, including prokaryotic cells, eukaryotic cells, mammalian cells,insect cells, or plant cells. As representative examples of appropriatehosts, there may be mentioned: bacterial cells, such as E. coli,Streptomyces, Bacillus subtilis, Salmonella typhimurium and variousspecies within the genera Pseudomonas, Streptomyces, and Staphylococcus,fungal cells, such as yeast, insect cells such as Drosophila S2 andSpodoptera Sf9, animal cells such as CHO, COS or Bowes melanoma, andadenoviruses. The selection of an appropriate host is within theabilities of those skilled in the art.

The vector may be introduced into the host cells using any of a varietyof techniques, including transformation, transfection, transduction,viral infection, gene guns, or Ti-mediated gene transfer. Particularmethods include calcium phosphate transfection, DEAE-Dextran mediatedtransfection, lipofection, or electroporation (Davis, L., Dibner, M.,Battey, I., Basic Methods in Molecular Biology, (1986)).

Where appropriate, the engineered host cells can be cultured inconventional nutrient media modified as appropriate for activatingpromoters, selecting transformants or amplifying the genes of theinvention. Following transformation of a suitable host strain and growthof the host strain to an appropriate cell density, the selected promotermay be induced by appropriate means (e.g., temperature shift or chemicalinduction) and the cells may be cultured for an additional period toallow them to produce the desired polypeptide or fragment thereof.

Cells are typically harvested by centrifugation, disrupted by physicalor chemical means, and the resulting crude extract is retained forfurther purification. Microbial cells employed for expression ofproteins can be disrupted by any convenient method, includingfreeze-thaw cycling, sonication, mechanical disruption, or use of celllysing agents. Such methods are well known to those skilled in the art.The expressed polypeptide or fragment thereof can be recovered andpurified from recombinant cell cultures by methods including ammoniumsulfate or ethanol precipitation, acid extraction, anion or cationexchange chromatography, phosphocellulose chromatography, hydrophobicinteraction chromatography, affinity chromatography, hydroxylapatitechromatography and lectin chromatography. Protein refolding steps can beused, as necessary, in completing configuration of the polypeptide. Ifdesired, high performance liquid chromatography (HPLC) can be employedfor final purification steps.

Various mammalian cell culture systems can also be employed to expressrecombinant protein. Examples of mammalian expression systems includethe COS-7 lines of monkey kidney fibroblasts (described by Gluzman,Cell, 23:175, 1981), and other cell lines capable of expressing proteinsfrom a compatible vector, such as the C127, 3T3, CHO, HeLa and BHK celllines.

The constructs in host cells can be used in a conventional manner toproduce the gene product encoded by the recombinant sequence. Dependingupon the host employed in a recombinant production procedure, thepolypeptides produced by host cells containing the vector may beglycosylated or may be non-glycosylated. Polypeptides of the inventionmay or may not also include an initial methionine amino acid residue.

Alternatively, the polypeptides of SEQ ID NO: 2, and sequencessubstantially identical thereto, or fragments comprising at least 5, 10,15, 20, 25, 30, 35, 40, 50, 75, 100, or 150 consecutive amino acidsthereof can be synthetically produced by conventional peptidesynthesizers. In other embodiments, fragments or portions of thepolypeptides may be employed for producing the corresponding full-lengthpolypeptide by peptide synthesis; therefore, the fragments may beemployed as intermediates for producing the full-length polypeptides.

Cell-free translation systems can also be employed to produce one of thepolypeptides of SEQ ID NO: 2, and sequences substantially identicalthereto, or fragments comprising at least 5, 10, 15, 20, 25, 30, 35, 40,50, 75, 100, or 150 consecutive amino acids thereof using mRNAstranscribed from a DNA construct comprising a promoter operably linkedto a nucleic acid encoding the polypeptide or fragment thereof. In someembodiments, the DNA construct may be linearized prior to conducting anin vitro transcription reaction. The transcribed mRNA is then incubatedwith an appropriate cell-free translation extract, such as a rabbitreticulocyte extract, to produce the desired polypeptide or fragmentthereof.

The invention also relates to variants of the polypeptides of SEQ ID NO:2, and sequences substantially identical thereto, or fragmentscomprising at least 5, 10, 15, 20, 25, 30, 35, 40, 50, 75, 100, or 150consecutive amino acids thereof. The term “variant” includes derivativesor analogs of these polypeptides. In particular, the variants may differin amino acid sequence from the polypeptides of SEQ ID NO: 2, andsequences substantially identical thereto, by one or more substitutions,additions, deletions, fusions and truncations, which may be present inany combination.

The variants may be naturally occurring or created in vitro. Inparticular, such variants may be created using genetic engineeringtechniques such as site directed mutagenesis, random chemicalmutagenesis, Exonuclease III deletion procedures, and standard cloningtechniques. Alternatively, such variants, fragments, analogs, orderivatives may be created using chemical synthesis or modificationprocedures.

Other methods of making variants are also familiar to those skilled inthe art. These include procedures in which nucleic acid sequencesobtained from natural isolates are modified to generate nucleic acidswhich encode polypeptides having characteristics which enhance theirvalue in industrial or laboratory applications. In such procedures, alarge number of variant sequences having one or more nucleotidedifferences with respect to the sequence obtained from the naturalisolate are generated and characterized. Typically, these nucleotidedifferences result in amino acid changes with respect to thepolypeptides encoded by the nucleic acids from the natural isolates.

For example, variants may be created using error prone PCR. In errorprone PCR, PCR is performed under conditions where the copying fidelityof the DNA polymerase is low, such that a high rate of point mutationsis obtained along the entire length of the PCR product. Error prone PCRis described in Leung, D. W., et al., Technique, 1:11-15, 1989) andCaldwell, R. C. & Joyce G. F., PCR Methods Applic., 2:28-33, 1992, thedisclosure of which is incorporated herein by reference in its entirety.Briefly, in such procedures, nucleic acids to be mutagenized are mixedwith PCR primers, reaction buffer, MgCl₂, MnCl₂, Taq polymerase and anappropriate concentration of dNTPs for achieving a high rate of pointmutation along the entire length of the PCR product. For example, thereaction may be performed using 20 fmoles of nucleic acid to bemutagenized, 30 pmole of each PCR primer, a reaction buffer comprising50 mM KCl, 10 mM Tris HCl (pH 8.3) and 0.01% gelatin, 7 mM MgCl₂, 0.5 mMMnCl₂, 5 units of Taq polymerase, 0.2 mM dGTP, 0.2 mM dATP, 1 mM dCTP,and 1 mM dTTP. PCR may be performed for 30 cycles of 94° C. for 1 min,45° C. for 1 min, and 72° C. for 1 min. However, it will be appreciatedthat these parameters may be varied as appropriate. The mutagenizednucleic acids are cloned into an appropriate vector and the activitiesof the polypeptides encoded by the mutagenized nucleic acids isevaluated.

Variants may also be created using oligonucleotide directed mutagenesisto generate site-specific mutations in any cloned DNA of interest.Oligonucleotide mutagenesis is described in Reidhaar-Olson, J. F. &Sauer, R. T., et al., Science, 241:53-57, 1988, the disclosure of whichis incorporated herein by reference in its entirety. Briefly, in suchprocedures a plurality of double stranded oligonucleotides bearing oneor more mutations to be introduced into the cloned DNA are synthesizedand inserted into the cloned DNA to be mutagenized. Clones containingthe mutagenized DNA are recovered and the activities of the polypeptidesthey encode are assessed.

Another method for generating variants is assembly PCR. Assembly PCRinvolves the assembly of a PCR product from a mixture of small DNAfragments. A large number of different PCR reactions occur in parallelin the same vial, with the products of one reaction priming the productsof another reaction. Assembly PCR is described in U.S. Pat. No.5,965,408, filed Jul. 9, 1996, entitled, “Method of DNA Reassembly byInterrupting Synthesis”, the disclosure of which is incorporated hereinby reference in its entirety.

Still another method of generating variants is sexual PCR mutagenesis.In sexual PCR mutagenesis, forced homologous recombination occursbetween DNA molecules of different but highly related DNA sequence invitro, as a result of random fragmentation of the DNA molecule based onsequence homology, followed by fixation of the crossover by primerextension in a PCR reaction. Sexual PCR mutagenesis is described inStemmer, W. P., PNAS, USA, 91:10747-10751, 1994, the disclosure of whichis incorporated herein by reference. Briefly, in such procedures aplurality of nucleic acids to be recombined are digested with DNAse togenerate fragments having an average size of 50-200 nucleotides.Fragments of the desired average size are purified and resuspended in aPCR mixture. PCR is conducted under conditions which facilitaterecombination between the nucleic acid fragments. For example, PCR maybe performed by resuspending the purified fragments at a concentrationof 10-30 ng/:1 in a solution of 0.2 mM of each dNTP, 2.2 mM MgCl2, 50 mMKCL, 10 mM Tris HCl, pH 9.0, and 0.1% Triton X-100. 2.5 units of Taqpolymerase per 100:1 of reaction mixture is added and PCR is performedusing the following regime: 94° C. for 60 seconds, 94° C. for 30seconds, 50-55° C. for 30 seconds, 72° C. for 30 seconds (30-45 times)and 72° C. for 5 minutes. However, it will be appreciated that theseparameters may be varied as appropriate. In some embodiments,oligonucleotides may be included in the PCR reactions. In otherembodiments, the Klenow fragment of DNA polymerase I may be used in afirst set of PCR reactions and Taq polymerase may be used in asubsequent set of PCR reactions. Recombinant sequences are isolated andthe activities of the polypeptides they encode are assessed.

Variants may also be created by in vivo mutagenesis. In someembodiments, random mutations in a sequence of interest are generated bypropagating the sequence of interest in a bacterial strain, such as anE. coli strain, which, carries mutations in one or more of the DNArepair pathways. Such “mutator” strains have a higher random mutationrate than that of a wild-type parent. Propagating the DNA in one ofthese strains will eventually generate random mutations within the DNA.Mutator strains suitable for use for in vivo mutagenesis are describedin PCT Publication No. WO 91/16427, published Oct. 31, 1991, entitled“Methods for Phenotype Creation from Multiple Gene Populations” thedisclosure of which is incorporated herein by reference in its entirety.

Variants may also be generated using cassette mutagenesis. In cassettemutagenesis a small region of a double stranded DNA molecule is replacedwith a synthetic oligonucleotide “cassette” that differs from the nativesequence. The oligonucleotide often contains completely and/or partiallyrandomized native sequence.

Recursive ensemble mutagenesis may also be used to generate variants.Recursive ensemble mutagenesis is an algorithm for protein engineering(protein mutagenesis) developed to produce diverse populations ofphenotypically related mutants whose members differ in amino acidsequence. This method uses a feedback mechanism to control successiverounds of combinatorial cassette mutagenesis. Recursive ensemblemutagenesis is described in Arkin, A. P. and Youvan, D. C., PNAS, USA,89:7811-7815, 1992, the disclosure of which is incorporated herein byreference in its entirety.

In some embodiments, variants are created using exponential ensemblemutagenesis. Exponential ensemble mutagenesis is a process forgenerating combinatorial libraries with a high percentage of unique andfunctional mutants, wherein small groups of residues are randomized inparallel to identify, at each altered position, amino acids which leadto functional proteins. Exponential ensemble mutagenesis is described inDelegrave, S. and Youvan, D. C., Biotechnology Research, 11:1548-1552,1993, the disclosure of which incorporated herein by reference in itsentirety. Random and site-directed mutagenesis are described in Arnold,F. H., Current Opinion in Biotechnology, 4:450-455, 1993, the disclosureof which is incorporated herein by reference in its entirety.

In some embodiments, the variants are created using shuffling procedureswherein portions of a plurality of nucleic acids which encode distinctpolypeptides are fused together to create chimeric nucleic acidsequences which encode chimeric polypeptides as described in U.S. Pat.No. 5,965,408, filed Jul. 9, 1996, entitled, “Method of DNA Reassemblyby Interrupting Synthesis”, and U.S. Pat. No. 5,939,250, filed May 22,1996, entitled, “Production of Enzymes Having Desired Activities byMutagenesis”, both of which are incorporated herein by reference.

The variants of the polypeptides of SEQ ID NO: 2 may be variants inwhich one or more of the amino acid residues of the polypeptides of theSEQ ID NO: 2 are substituted with a conserved or non-conserved aminoacid residue (preferably a conserved amino acid residue) and suchsubstituted amino acid residue may or may not be one encoded by thegenetic code.

Conservative substitutions are those that substitute a given amino acidin a polypeptide by another amino acid of like characteristics.Typically seen as conservative substitutions are the followingreplacements: replacements of an aliphatic amino acid such as Ala, Val,Leu and Ile with another aliphatic amino acid; replacement of a Ser witha Thr or vice versa; replacement of an acidic residue such as Asp andGlu with another acidic residue; replacement of a residue bearing anamide group, such as Asn and Gln, with another residue bearing an amidegroup; exchange of a basic residue such as Lys and Arg with anotherbasic residue; and replacement of an aromatic residue such as Phe, Tyrwith another aromatic residue.

Other variants are those in which one or more of the amino acid residuesof the polypeptides of the SEQ ID NO: 2 includes a substituent group.

Still other variants are those in which the polypeptide is associatedwith another compound, such as a compound to increase the half-life ofthe polypeptide (for example, polyethylene glycol).

Additional variants are those in which additional amino acids are fusedto the polypeptide, such as a leader sequence, a secretory sequence, aproprotein sequence or a sequence which facilitates purification,enrichment, or stabilization of the polypeptide.

In some embodiments, the fragments, derivatives and analogs retain thesame biological function or activity as the polypeptides of SEQ ID NO:2, and sequences substantially identical thereto. In other embodiments,the fragment, derivative, or analog includes a proprotein, such that thefragment, derivative, or analog can be activated by cleavage of theproprotein portion to produce an active polypeptide.

Another aspect of the invention is polypeptides or fragments thereofwhich have at least about 70%, at least about 80%, at least about 85%,at least about 90%, at least about 95%, or more than about 95% homologyto one of the polypeptides of SEQ ID NO: 2, and sequences substantiallyidentical thereto, or a fragment comprising at least 5, 10, 15, 20, 25,30, 35, 40, 50, 75, 100, or 150 consecutive amino acids thereof.Homology may be determined using any of the programs described abovewhich aligns the polypeptides or fragments being compared and determinesthe extent of amino acid identity or similarity between them. It will beappreciated that amino acid “homology” includes conservative amino acidsubstitutions such as those described above.

The polypeptides or fragments having homology to one of the polypeptidesof SEQ ID NO: 2, and sequences substantially identical thereto, or afragment comprising at least about 5, 10, 15, 20, 25, 30, 35, 40, 50,75, 100, or 150 consecutive amino acids thereof may be obtained byisolating the nucleic acids encoding them using the techniques describedabove.

Alternatively, the homologous polypeptides or fragments may be obtainedthrough biochemical enrichment or purification procedures. The sequenceof potentially homologous polypeptides or fragments may be determined byproteolytic digestion, gel electrophoresis and/or microsequencing. Thesequence of the prospective homologous polypeptide or fragment can becompared to one of the polypeptides of SEQ ID NO: 2, and sequencessubstantially identical thereto, or a fragment comprising at least about5, 10, 15, 20, 25, 30, 35, 40, 50, 75, 100, or 150 consecutive aminoacids thereof using any of the programs described above.

Another aspect of the invention is an assay for identifying fragments orvariants of SEQ ID NO: 2, and sequences substantially identical thereto,which retain the enzymatic function of the polypeptides of SEQ ID NO: 2,and sequences substantially identical thereto. For example the fragmentsor variants of said polypeptides, may be used to catalyze biochemicalreactions, which indicate that the fragment or variant retains theenzymatic activity of the polypeptides in the SEQ ID NO: 2.

The assay for determining if fragments of variants retain the enzymaticactivity of the polypeptides of SEQ ID NO: 2, and sequencessubstantially identical thereto includes the steps of; contacting thepolypeptide fragment or variant with a substrate molecule underconditions which allow the polypeptide fragment or variant to function,and detecting either a decrease in the level of substrate or an increasein the level of the specific reaction product of the reaction betweenthe polypeptide and substrate.

The polypeptides of SEQ ID NO: 2, and sequences substantially identicalthereto or fragments comprising at least 5, 10, 15, 20, 25, 30, 35, 40,50, 75, 100, or 150 consecutive amino acids thereof may be used in avariety of applications. For example, the polypeptides or fragmentsthereof may be used to catalyze biochemical reactions. In accordancewith one aspect of the invention, there is provided a process forutilizing the polypeptides of SEQ ID NO: 2, and sequences substantiallyidentical thereto or polynucleotides encoding such polypeptides forhydrolyzing glycosidic linkages. In such procedures, a substancecontaining a glycosidic linkage (e.g., a starch) is contacted with oneof the polypeptides of SEQ ID NO: 2, or sequences substantiallyidentical thereto under conditions which facilitate the hydrolysis ofthe glycosidic linkage.

The polypeptides of SEQ ID NO: 2, and sequences substantially identicalthereto or fragments comprising at least 5, 10, 15, 20, 25, 30, 35, 40,50, 75, 100, or 150 consecutive amino acids thereof, may also be used togenerate antibodies which bind specifically to the polypeptides orfragments. The resulting antibodies may be used in immunoaffinitychromatography procedures to isolate or purify the polypeptide or todetermine whether the polypeptide is present in a biological sample. Insuch procedures, a protein preparation, such as an extract, or abiological sample is contacted with an antibody capable of specificallybinding to one of the polypeptides of SEQ ID NO: 2, and sequencessubstantially identical thereto, or fragments comprising at least 5, 10,15, 20, 25, 30, 35, 40, 50, 75, 100, or 150 consecutive amino acidsthereof.

In immunoaffinity procedures, the antibody is attached to a solidsupport, such as a bead or other column matrix. The protein preparationis placed in contact with the antibody under conditions in which theantibody specifically binds to one of the polypeptides of SEQ ID NO: 2,and sequences substantially identical thereto, or fragment thereof.After a wash to remove non-specifically bound proteins, the specificallybound polypeptides are eluted.

The ability of proteins in a biological sample to bind to the antibodymay be determined using any of a variety of procedures familiar to thoseskilled in the art. For example, binding may be determined by labelingthe antibody with a detectable label such as a fluorescent agent, anenzymatic label, or a radioisotope. Alternatively, binding of theantibody to the sample may be detected using a secondary antibody havingsuch a detectable label thereon. Particular assays include ELISA assays,sandwich assays, radioimmunoassays, and Western Blots.

Polyclonal antibodies generated against the polypeptides of SEQ ID NO:2, and sequences substantially identical thereto, or fragmentscomprising at least 5, 10, 15, 20, 25, 30, 35, 40, 50, 75, 100, or 150consecutive amino acids thereof can be obtained by direct injection ofthe polypeptides into an animal or by administering the polypeptides toan animal, for example, a nonhuman. The antibody so obtained will thenbind the polypeptide itself. In this manner, even a sequence encodingonly a fragment of the polypeptide can be used to generate antibodieswhich may bind to the whole native polypeptide. Such antibodies can thenbe used to isolate the polypeptide from cells expressing thatpolypeptide.

For preparation of monoclonal antibodies, any technique which providesantibodies produced by continuous cell line cultures can be used.Examples include the hybridoma technique (Kohler and Milstein, Nature,256:495-497, 1975, the disclosure of which is incorporated herein byreference), the trioma technique, the human B-cell hybridoma technique(Kozbor et al., Immunology Today 4:72, 1983, the disclosure of which isincorporated herein by reference), and the EBV-hybridoma technique(Cole, et al., 1985, in Monoclonal Antibodies and Cancer Therapy, AlanR. Liss, Inc., pp. 77-96, the disclosure of which is incorporated hereinby reference).

Techniques described for the production of single chain antibodies (U.S.Pat. No. 4,946,778, the disclosure of which is incorporated herein byreference) can be adapted to produce single chain antibodies to thepolypeptides of SEQ ID NO: 2, and sequences substantially identicalthereto, or fragments comprising at least 5, 10, 15, 20, 25, 30, 35, 40,50, 75, 100, or 150 consecutive amino acids thereof. Alternatively,transgenic mice may be used to express humanized antibodies to thesepolypeptides or fragments thereof.

Antibodies generated against the polypeptides of SEQ ID NO: 2, andsequences substantially identical thereto, or fragments comprising atleast 5, 10, 15, 20, 25, 30, 35, 40, 50, 75, 100, or 150 consecutiveamino acids thereof may be used in screening for similar polypeptidesfrom other organisms and samples. In such techniques, polypeptides fromthe organism are contacted with the antibody and those polypeptideswhich specifically bind the antibody are detected. Any of the proceduresdescribed above may be used to detect antibody binding. One suchscreening assay is described in “Methods for Measuring CellulaseActivities”, Methods in Enzymology, Vol 160, pp. 87-116, which is herebyincorporated by reference in its entirety.

As used herein the term “nucleic acid sequence as set forth in SEQ IDNO: 1” encompasses the nucleotide sequences of SEQ ID NO: 1, andsequences substantially identical thereto, as well as sequenceshomologous to SEQ ID NO: 1, and fragments thereof and sequencescomplementary to all of the preceding sequences. The fragments includeportions of SEQ ID NO: 1, comprising at least 10, 15, 20, 25, 30, 35,40, 50, 75, 100, 150, 200, 300, 400, or 500 consecutive nucleotides ofSEQ ID NO: 1, and sequences substantially identical thereto. Homologoussequences and fragments of SEQ ID NO: 1, and sequences substantiallyidentical thereto, refer to a sequence having at least 99%, 98%, 97%,96%, 95%, 90%, 85%, 80%, 75% or 70% homology to these sequences.Homology may be determined using any of the computer programs andparameters described herein, including FASTA version 3.0t78 with thedefault parameters. Homologous sequences also include RNA sequences inwhich uridines replace the thymines in the nucleic acid sequences as setforth in the SEQ ID NO: 1. The homologous sequences may be obtainedusing any of the procedures described herein or may result from thecorrection of a sequencing error. It will be appreciated that thenucleic acid sequences as set forth in SEQ ID NO: 1, and sequencessubstantially identical thereto, can be represented in the traditionalsingle character format (See the inside back cover of Stryer, Lubert.Biochemistry, 3^(rd) edition. W. H Freeman & Co., New York.) or in anyother format which records the identity of the nucleotides in asequence.

As used herein the term “a polypeptide sequence as set forth in SEQ IDNO: 2” encompasses the polypeptide sequence of SEQ ID NO: 2, andsequences substantially identical thereto, which are encoded by asequence as set forth in SEQ ID NO: 1, polypeptide sequences homologousto the polypeptides of SEQ ID NO: 2, and sequences substantiallyidentical thereto, or fragments of any of the preceding sequences.Homologous polypeptide sequences refer to a polypeptide sequence havingat least 99%, 98%, 97%, 96%, 95%, 90%, 85%, 80%, 75% or 70% homology toone of the polypeptide sequences of the SEQ ID NO: 2. Homology may bedetermined using any of the computer programs and parameters describedherein, including FASTA version 3.0t78 with the default parameters orwith any modified parameters. The homologous sequences may be obtainedusing any of the procedures described herein or may result from thecorrection of a sequencing error. The polypeptide fragments comprise atleast 5, 10, 15, 20, 25, 30, 35, 40, 50, 75, 100, or 150 consecutiveamino acids of the polypeptides of SEQ ID NO: 2, and sequencessubstantially identical thereto. It will be appreciated that thepolypeptide codes as set forth in SEQ ID NO: 2, and sequencessubstantially identical thereto, can be represented in the traditionalsingle character format or three letter format (See the inside backcover of Starrier, Lubert. Biochemistry, 3^(rd) edition. W. H Freeman &Co., New York.) or in any other format which relates the identity of thepolypeptides in a sequence.

It will be appreciated by those skilled in the art that a nucleic acidsequence as set forth SEQ ID NO: 1 and a polypeptide sequence as setforth in SEQ ID NO: 2 can be stored, recorded, and manipulated on anymedium which can be read and accessed by a computer. As used herein, thewords “recorded” and “stored” refer to a process for storing informationon a computer medium. A skilled artisan can readily adopt any of thepresently known methods for recording information on a computer readablemedium to generate manufactures comprising one or more of the nucleicacid sequences as set forth in SEQ ID NO: 1, and sequences substantiallyidentical thereto, one or more of the polypeptide sequences as set forthin SEQ ID NO: 2, and sequences substantially identical thereto. Anotheraspect of the invention is a computer readable medium having recordedthereon at least 2, 5, 10, 15, or 20 nucleic acid sequences as set forthin SEQ ID NO: 1, and sequences substantially identical thereto.

Another aspect of the invention is a computer readable medium havingrecorded thereon one or more of the nucleic acid sequences as set forthin SEQ ID NO: 1, and sequences substantially identical thereto. Anotheraspect of the invention is a computer readable medium having recordedthereon one or more of the polypeptide sequences as set forth in SEQ IDNO: 2, and sequences substantially identical thereto. Another aspect ofthe invention is a computer readable medium having recorded thereon atleast 2, 5, 10, 15, or 20 of the sequences as set forth above.

Computer readable media include magnetically readable media, opticallyreadable media, electronically readable media and magnetic/opticalmedia. For example, the computer readable media may be a hard disk, afloppy disk, a magnetic tape, CD-ROM, Digital Versatile Disk (DVD),Random Access Memory (RAM), or Read Only Memory (ROM) as well as othertypes of other media known to those skilled in the art.

Embodiments of the invention include systems (e.g., internet basedsystems), particularly computer systems which store and manipulate thesequence information described herein. One example of a computer system100 is illustrated in block diagram form in FIG. 2. As used herein, “acomputer system” refers to the hardware components, software components,and data storage components used to analyze a nucleotide sequence of anucleic acid sequence as set forth in SEQ ID NO: 1, and sequencessubstantially identical thereto, or a polypeptide sequence as set forthin the SEQ ID NO: 2. The computer system 100 typically includes aprocessor for processing, accessing and manipulating the sequence data.The processor 105 can be any well-known type of central processing unit,such as, for example, the Pentium III from Intel Corporation, or similarprocessor from Sun, Motorola, Compaq, AMD or International BusinessMachines.

Typically the computer system 100 is a general purpose system thatcomprises the processor 105 and one or more internal data storagecomponents 110 for storing data, and one or more data retrieving devicesfor retrieving the data stored on the data storage components. A skilledartisan can readily appreciate that any one of the currently availablecomputer systems are suitable.

In one particular embodiment, the computer system 100 includes aprocessor 105 connected to a bus which is connected to a main memory 115(preferably implemented as RAM) and one or more internal data storagedevices 110, such as a hard drive and/or other computer readable mediahaving data recorded thereon. In some embodiments, the computer system100 further includes one or more data retrieving device 118 for readingthe data stored on the internal data storage devices 110.

The data retrieving device 118 may represent, for example, a floppy diskdrive, a compact disk drive, a magnetic tape drive, or a modem capableof connection to a remote data storage system (e.g., via the internet)etc. In some embodiments, the internal data storage device 110 is aremovable computer readable medium such as a floppy disk, a compactdisk, a magnetic tape, etc. containing control logic and/or datarecorded thereon. The computer system 100 may advantageously include orbe programmed by appropriate software for reading the control logicand/or the data from the data storage component once inserted in thedata retrieving device.

The computer system 100 includes a display 120 which is used to displayoutput to a computer user. It should also be noted that the computersystem 100 can be linked to other computer systems 125 a-c in a networkor wide area network to provide centralized access to the computersystem 100.

Software for accessing and processing the nucleotide sequences of anucleic acid sequence as set forth in SEQ ID NO: 1, and sequencessubstantially identical thereto, or a polypeptide sequence as set forthin SEQ ID NO: 2, and sequences substantially identical thereto, (such assearch tools, compare tools, and modeling tools etc.) may reside in mainmemory 115 during execution.

In some embodiments, the computer system 100 may further comprise asequence comparison algorithm for comparing a nucleic acid sequence asset forth in SEQ ID NO: 1, and sequences substantially identicalthereto, or a polypeptide sequence as set forth in SEQ ID NO: 2, andsequences substantially identical thereto, stored on a computer readablemedium to a reference nucleotide or polypeptide sequence(s) stored on acomputer readable medium. A “sequence comparison algorithm” refers toone or more programs which are implemented (locally or remotely) on thecomputer system 100 to compare a nucleotide sequence with othernucleotide sequences and/or compounds stored within a data storagemeans. For example, the sequence comparison algorithm may compare thenucleotide sequences of a nucleic acid sequence as set forth in SEQ IDNO: 1, and sequences substantially identical thereto, or a polypeptidesequence as set forth in SEQ ID NO: 2, and sequences substantiallyidentical thereto, stored on a computer readable medium to referencesequences stored on a computer readable medium to identify homologies orstructural motifs. Various sequence comparison programs identifiedelsewhere in this patent specification are particularly contemplated foruse in this aspect of the invention. Protein and/or nucleic acidsequence homologies may be evaluated using any of the variety ofsequence comparison algorithms and programs known in the art. Suchalgorithms and programs include, but are by no means limited to,TBLASTN, BLASTP, FASTA, TFASTA, and CLUSTALW (Pearson and Lipman, Proc.Natl. Acad. Sci. USA 85(8):2444-2448, 1988; Altschul et al., J. Mol.Biol. 215(3):403-410, 1990; Thompson et al., Nucleic Acids Res.22(2):4673-4680, 1994; Higgins et al., Methods Enzymol. 266:383-402,1996; Altschul et al., J. Mol. Biol. 215(3):403-410, 1990; Altschul etal., Nature Genetics 3:266-272, 1993).

Homology or identity is often measured using sequence analysis software(e.g., Sequence Analysis Software Package of the Genetics ComputerGroup, University of Wisconsin Biotechnology Center, 1710 UniversityAvenue, Madison, Wis. 53705). Such software matches similar sequences byassigning degrees of homology to various deletions, substitutions andother modifications. The terms “homology” and “identity” in the contextof two or more nucleic acids or polypeptide sequences, refer to two ormore sequences or subsequences that are the same or have a specifiedpercentage of amino acid residues or nucleotides that are the same whencompared and aligned for maximum correspondence over a comparison windowor designated region as measured using any number of sequence comparisonalgorithms or by manual alignment and visual inspection.

For sequence comparison, typically one sequence acts as a referencesequence, to which test sequences are compared. When using a sequencecomparison algorithm, test and reference sequences are entered into acomputer, subsequence coordinates are designated, if necessary, andsequence algorithm program parameters are designated. Default programparameters can be used, or alternative parameters can be designated. Thesequence comparison algorithm then calculates the percent sequenceidentities for the test sequences relative to the reference sequence,based on the program parameters.

A “comparison window”, as used herein, includes reference to a segmentof any one of the number of contiguous positions selected from the groupconsisting of from 20 to 600, usually about 50 to about 200, moreusually about 100 to about 150 in which a sequence may be compared to areference sequence of the same number of contiguous positions after thetwo sequences are optimally aligned. Methods of alignment of sequencefor comparison are well-known in the art. Optimal alignment of sequencesfor comparison can be conducted, e.g., by the local homology algorithmof Smith & Waterman, Adv. Appl. Math. 2:482, 1981, by the homologyalignment algorithm of Needleman & Wunsch, J. Mol. Biol 48:443, 1970, bythe search for similarity method of person & Lipman, Proc. Nat'l. Acad.Sci. USA 85:2444, 1988, by computerized implementations of thesealgorithms (GAP, BESTFIT, FASTA, and TFASTA in the Wisconsin GeneticsSoftware Package, Genetics Computer Group, 575 Science Dr., Madison,Wis.), or by manual alignment and visual inspection. Other algorithmsfor determining homology or identity include, for example, in additionto a BLAST program (Basic Local Alignment Search Tool at the NationalCenter for Biological Information), ALIGN, AMAS (Analysis of MultiplyAligned Sequences), AMPS (Protein Multiple Sequence Alignment), ASSET(Aligned Segment Statistical Evaluation Tool), BANDS, BESTSCOR, BIOSCAN(Biological Sequence Comparative Analysis Node), BLIMPS (BLocks IMProvedSearcher), FASTA, Intervals & Points, BMB, CLUSTAL V, CLUSTAL W,CONSENSUS, LCONSENSUS, WCONSENSUS, Smith-Waterman algorithm, DARWIN, LasVegas algorithm, FNAT (Forced Nucleotide Alignment Tool), Framealign,Framesearch, DYNAMIC, FILTER, FSAP (Fristensky Sequence AnalysisPackage), GAP (Global Alignment Program), GENAL, GIBBS, GenQuest, ISSC(Sensitive Sequence Comparison), LALIGN (Local Sequence Alignment), LCP(Local Content Program), MACAW (Multiple Alignment Construction &Analysis Workbench), MAP (Multiple Alignment Program), MBLKP, MBLKN,PIMA (Pattern-Induced Multi-sequence Alignment), SAGA (SequenceAlignment by Genetic Algorithm) and WHAT-IF. Such alignment programs canalso be used to screen genome databases to identify polynucleotidesequences having substantially identical sequences. A number of genomedatabases are available, for example, a substantial portion of the humangenome is available as part of the Human Genome Sequencing Project. Atleast twenty-one other genomes have already been sequenced, including,for example, M. genitalium (Fraser et al., 1995), M. jannaschii (Bult etal., 1996), H. influenzae (Fleischmann et al., 1995), E. coli (Blattneret al., 1997), and yeast (S. cerevisiae) (Mewes et al., 1997), and D.melanogaster (Adams et al., 2000). Significant progress has also beenmade in sequencing the genomes of model organism, such as mouse, C.elegans, and Arabadopsis sp. Several databases containing genomicinformation annotated with some functional information are maintained bydifferent organization, and are accessible via the interne.

One example of a useful algorithm is BLAST and BLAST 2.0 algorithms,which are described in Altschul et al., Nuc. Acids Res. 25:3389-3402,1977, and Altschul et al., J. Mol. Biol. 215:403-410, 1990,respectively. Software for performing BLAST analyses is publiclyavailable through the National Center for Biotechnology Information.This algorithm involves first identifying high scoring sequence pairs(HSPs) by identifying short words of length W in the query sequence,which either match or satisfy some positive-valued threshold score Twhen aligned with a word of the same length in a database sequence. T isreferred to as the neighborhood word score threshold (Altschul et al.,supra). These initial neighborhood word hits act as seeds for initiatingsearches to find longer HSPs containing them. The word hits are extendedin both directions along each sequence for as far as the cumulativealignment score can be increased. Cumulative scores are calculatedusing, for nucleotide sequences, the parameters M (reward score for apair of matching residues; always >0). For amino acid sequences, ascoring matrix is used to calculate the cumulative score. Extension ofthe word hits in each direction are halted when: the cumulativealignment score falls off by the quantity X from its maximum achievedvalue; the cumulative score goes to zero or below, due to theaccumulation of one or more negative-scoring residue alignments; or theend of either sequence is reached. The BLAST algorithm parameters W, T,and X determine the sensitivity and speed of the alignment. The BLASTNprogram (for nucleotide sequences) uses as defaults a wordlength (W) of11, an expectation (E) of 10, M=5, N=−4 and a comparison of bothstrands. For amino acid sequences, the BLASTP program uses as defaults awordlength of 3, and expectations (E) of 10, and the BLOSUM62 scoringmatrix (see Henikoff & Henikoff, Proc. Natl. Acad. Sci. USA 89:10915,1989) alignments (B) of 50, expectation (E) of 10, M=5, N=−4, and acomparison of both strands.

The BLAST algorithm also performs a statistical analysis of thesimilarity between two sequences (see, e.g., Karlin & Altschul, Proc.Natl. Acad. Sci. USA 90:5873, 1993). One measure of similarity providedby BLAST algorithm is the smallest sum probability (P(N)), whichprovides an indication of the probability by which a match between twonucleotide or amino acid sequences would occur by chance. For example, anucleic acid is considered similar to a references sequence if thesmallest sum probability in a comparison of the test nucleic acid to thereference nucleic acid is less than about 0.2, more preferably less thanabout 0.01, and most preferably less than about 0.001.

In one embodiment, protein and nucleic acid sequence homologies areevaluated using the Basic Local Alignment Search Tool (“BLAST”) Inparticular, five specific BLAST programs are used to perform thefollowing task:

-   -   (1) BLASTP and BLAST3 compare an amino acid query sequence        against a protein sequence database;    -   (2) BLASTN compares a nucleotide query sequence against a        nucleotide sequence database;    -   (3) BLASTX compares the six-frame conceptual translation        products of a query nucleotide sequence (both strands) against a        protein sequence database;    -   (4) TBLASTN compares a query protein sequence against a        nucleotide sequence database translated in all six reading        frames (both strands); and    -   (5) TBLASTX compares the six-frame translations of a nucleotide        query sequence against the six-frame translations of a        nucleotide sequence database.

The BLAST programs identify homologous sequences by identifying similarsegments, which are referred to herein as “high-scoring segment pairs,”between a query amino or nucleic acid sequence and a test sequence whichis preferably obtained from a protein or nucleic acid sequence database.High-scoring segment pairs are preferably identified (i.e., aligned) bymeans of a scoring matrix, many of which are known in the art.Preferably, the scoring matrix used is the BLOSUM62 matrix (Gonnet etal., Science 256:1443-1445, 1992; Henikoff and Henikoff, Proteins17:49-61, 1993). Less preferably, the PAM or PAM250 matrices may also beused (see, e.g., Schwartz and Dayhoff, eds., 1978, Matrices forDetecting Distance Relationships: Atlas of Protein Sequence andStructure, Washington: National Biomedical Research Foundation). BLASTprograms are accessible through the U.S. National Library of Medicine.

The parameters used with the above algorithms may be adapted dependingon the sequence length and degree of homology studied. In someembodiments, the parameters may be the default parameters used by thealgorithms in the absence of instructions from the user.

FIG. 3 is a flow diagram illustrating one embodiment of a process 200for comparing a new nucleotide or protein sequence with a database ofsequences in order to determine the homology levels between the newsequence and the sequences in the database. The database of sequencescan be a private database stored within the computer system 100, or apublic database such as GENBANK that is available through the Internet.

The process 200 begins at a start state 201 and then moves to a state202 wherein the new sequence to be compared is stored to a memory in acomputer system 100. As discussed above, the memory could be any type ofmemory, including RAM or an internal storage device.

The process 200 then moves to a state 204 wherein a database ofsequences is opened for analysis and comparison. The process 200 thenmoves to a state 206 wherein the first sequence stored in the databaseis read into a memory on the computer. A comparison is then performed ata state 210 to determine if the first sequence is the same as the secondsequence. It is important to note that this step is not limited toperforming an exact comparison between the new sequence and the firstsequence in the database. Well-known methods are known to those of skillin the art for comparing two nucleotide or protein sequences, even ifthey are not identical. For example, gaps can be introduced into onesequence in order to raise the homology level between the two testedsequences. The parameters that control whether gaps or other featuresare introduced into a sequence during comparison are normally entered bythe user of the computer system.

Once a comparison of the two sequences has been performed at the state210, a determination is made at a decision state 210 whether the twosequences are the same. Of course, the term “same” is not limited tosequences that are absolutely identical. Sequences that are within thehomology parameters entered by the user will be marked as “same” in theprocess 200.

If a determination is made that the two sequences are the same, theprocess 200 moves to a state 214 wherein the name of the sequence fromthe database is displayed to the user. This state notifies the user thatthe sequence with the displayed name fulfills the homology constraintsthat were entered. Once the name of the stored sequence is displayed tothe user, the process 200 moves to a decision state 218 wherein adetermination is made whether more sequences exist in the database. Ifno more sequences exist in the database, then the process 200 terminatesat an end state 220. However, if more sequences do exist in thedatabase, then the process 200 moves to a state 224 wherein a pointer ismoved to the next sequence in the database so that it can be compared tothe new sequence. In this manner, the new sequence is aligned andcompared with every sequence in the database.

It should be noted that if a determination had been made at the decisionstate 212 that the sequences were not homologous, then the process 200would move immediately to the decision state 218 in order to determineif any other sequences were available in the database for comparison.

Accordingly, one aspect of the invention is a computer system comprisinga processor, a data storage device having stored thereon a nucleic acidsequence as set forth in SEQ ID NO: 1, and sequences substantiallyidentical thereto, or a polypeptide sequence as set forth in SEQ ID NO:2, and sequences substantially identical thereto, a data storage devicehaving retrievably stored thereon reference nucleotide sequences orpolypeptide sequences to be compared to a nucleic acid sequence as setforth in SEQ ID NO: 1, and sequences substantially identical thereto, ora polypeptide sequence as set forth in SEQ ID NO: 1, and sequencessubstantially identical thereto, and a sequence comparer for conductingthe comparison. The sequence comparer may indicate a homology levelbetween the sequences compared or identify structural motifs in theabove described nucleic acid code of SEQ ID NO: 1, and sequencessubstantially identical thereto, or a polypeptide sequence as set forthin SEQ ID NO: 2, and sequences substantially identical thereto, or itmay identify structural motifs in sequences which are compared to thesenucleic acid codes and polypeptide codes. In some embodiments, the datastorage device may have stored thereon the sequences of at least 2, 5,10, 15, 20, 25, 30 or 40 or more of the nucleic acid sequences as setforth in SEQ ID NO: 1, and sequences substantially identical thereto, orthe polypeptide sequences as set forth in SEQ ID NO: 2, and sequencessubstantially identical thereto.

Another aspect of the invention is a method for determining the level ofhomology between a nucleic acid sequence as set forth in SEQ ID NO: 1,and sequences substantially identical thereto, or a polypeptide sequenceas set forth in SEQ ID NO: 2, and sequences substantially identicalthereto, and a reference nucleotide sequence. The method includingreading the nucleic acid code or the polypeptide code and the referencenucleotide or polypeptide sequence through the use of a computer programwhich determines homology levels and determining homology between thenucleic acid code or polypeptide code and the reference nucleotide orpolypeptide sequence with the computer program. The computer program maybe any of a number of computer programs for determining homology levels,including those specifically enumerated herein, (e.g., BLAST2N with thedefault parameters or with any modified parameters). The method may beimplemented using the computer systems described above. The method mayalso be performed by reading at least 2, 5, 10, 15, 20, 25, 30 or 40 ormore of the above described nucleic acid sequences as set forth in theSEQ ID NO: 1, or the polypeptide sequences as set forth in the Group Bnucleic acid sequences through use of the computer program anddetermining homology between the nucleic acid codes or polypeptide codesand reference nucleotide sequences or polypeptide sequences.

FIG. 4 is a flow diagram illustrating one embodiment of a process 250 ina computer for determining whether two sequences are homologous. Theprocess 250 begins at a start state 252 and then moves to a state 254wherein a first sequence to be compared is stored to a memory. Thesecond sequence to be compared is then stored to a memory at a state256. The process 250 then moves to a state 260 wherein the firstcharacter in the first sequence is read and then to a state 262 whereinthe first character of the second sequence is read. It should beunderstood that if the sequence is a nucleotide sequence, then thecharacter would normally be either A, T, C, G or U. If the sequence is aprotein sequence, then it is preferably in the single letter amino acidcode so that the first and sequence sequences can be easily compared.

A determination is then made at a decision state 264 whether the twocharacters are the same. If they are the same, then the process 250moves to a state 268 wherein the next characters in the first and secondsequences are read. A determination is then made whether the nextcharacters are the same. If they are, then the process 250 continuesthis loop until two characters are not the same. If a determination ismade that the next two characters are not the same, the process 250moves to a decision state 274 to determine whether there are any morecharacters either sequence to read.

If there are not any more characters to read, then the process 250 movesto a state 276 wherein the level of homology between the first andsecond sequences is displayed to the user. The level of homology isdetermined by calculating the proportion of characters between thesequences that were the same out of the total number of sequences in thefirst sequence. Thus, if every character in a first 100 nucleotidesequence aligned with a every character in a second sequence, thehomology level would be 100%.

Alternatively, the computer program may be a computer program whichcompares the nucleotide sequences of a nucleic acid sequence as setforth in the invention, to one or more reference nucleotide sequences inorder to determine whether the nucleic acid code of SEQ ID NO: 1, andsequences substantially identical thereto, differs from a referencenucleic acid sequence at one or more positions. Optionally such aprogram records the length and identity of inserted, deleted orsubstituted nucleotides with respect to the sequence of either thereference polynucleotide or a nucleic acid sequence as set forth in SEQID NO: 1, and sequences substantially identical thereto. In oneembodiment, the computer program may be a program which determineswhether a nucleic acid sequence as set forth in SEQ ID NO: 1, andsequences substantially identical thereto, contains a single nucleotidepolymorphism (SNP) with respect to a reference nucleotide sequence.

Accordingly, another aspect of the invention is a method for determiningwhether a nucleic acid sequence as set forth in SEQ ID NO: 1, andsequences substantially identical thereto, differs at one or morenucleotides from a reference nucleotide sequence comprising the steps ofreading the nucleic acid code and the reference nucleotide sequencethrough use of a computer program which identifies differences betweennucleic acid sequences and identifying differences between the nucleicacid code and the reference nucleotide sequence with the computerprogram. In some embodiments, the computer program is a program whichidentifies single nucleotide polymorphisms. The method may beimplemented by the computer systems described above and the methodillustrated in FIG. 4. The method may also be performed by reading atleast 2, 5, 10, 15, 20, 25, 30, or 40 or more of the nucleic acidsequences as set forth in SEQ ID NO: 1, and sequences substantiallyidentical thereto, and the reference nucleotide sequences through theuse of the computer program and identifying differences between thenucleic acid codes and the reference nucleotide sequences with thecomputer program.

In other embodiments the computer based system may further comprise anidentifier for identifying features within a nucleic acid sequence asset forth in the SEQ ID NO: 1 or a polypeptide sequence as set forth inSEQ ID NO: 2, and sequences substantially identical thereto.

An “identifier” refers to one or more programs which identifies certainfeatures within a nucleic acid sequence as set forth in SEQ ID NO: 1,and sequences substantially identical thereto, or a polypeptide sequenceas set forth in SEQ ID NO: 2, and sequences substantially identicalthereto. In one embodiment, the identifier may comprise a program whichidentifies an open reading frame in a nucleic acid sequence as set forthin SEQ ID NO: 1, and sequences substantially identical thereto.

FIG. 5 is a flow diagram illustrating one embodiment of an identifierprocess 300 for detecting the presence of a feature in a sequence. Theprocess 300 begins at a start state 302 and then moves to a state 304wherein a first sequence that is to be checked for features is stored toa memory 115 in the computer system 100. The process 300 then moves to astate 306 wherein a database of sequence features is opened. Such adatabase would include a list of each feature's attributes along withthe name of the feature. For example, a feature name could be“Initiation Codon” and the attribute would be “ATG”. Another examplewould be the feature name “TAATAA Box” and the feature attribute wouldbe “TAATAA”. An example of such a database is produced by the Universityof Wisconsin Genetics Computer Group. Alternatively, the features may bestructural polypeptide motifs such as alpha helices, beta sheets, orfunctional polypeptide motifs such as enzymatic active sites,helix-turn-helix motifs or other motifs known to those skilled in theart.

Once the database of features is opened at the state 306, the process300 moves to a state 308 wherein the first feature is read from thedatabase. A comparison of the attribute of the first feature with thefirst sequence is then made at a state 310. A determination is then madeat a decision state 316 whether the attribute of the feature was foundin the first sequence. If the attribute was found, then the process 300moves to a state 318 wherein the name of the found feature is displayedto the user.

The process 300 then moves to a decision state 320 wherein adetermination is made whether move features exist in the database. If nomore features do exist, then the process 300 terminates at an end state324. However, if more features do exist in the database, then theprocess 300 reads the next sequence feature at a state 326 and loopsback to the state 310 wherein the attribute of the next feature iscompared against the first sequence.

It should be noted, that if the feature attribute is not found in thefirst sequence at the decision state 316, the process 300 moves directlyto the decision state 320 in order to determine if any more featuresexist in the database.

Accordingly, another aspect of the invention is a method of identifyinga feature within a nucleic acid sequence as set forth in SEQ ID NO: 1,and sequences substantially identical thereto, or a polypeptide sequenceas set forth in SEQ ID NO: 2, and sequences substantially identicalthereto, comprising reading the nucleic acid code(s) or polypeptidecode(s) through the use of a computer program which identifies featurestherein and identifying features within the nucleic acid code(s) withthe computer program. In one embodiment, computer program comprises acomputer program which identifies open reading frames. The method may beperformed by reading a single sequence or at least 2, 5, 10, 15, 20, 25,30, or 40 of the nucleic acid sequences as set forth in SEQ ID NO: 1,and sequences substantially identical thereto, or the polypeptidesequences as set forth in SEQ ID NO: 2, and sequences substantiallyidentical thereto, through the use of the computer program andidentifying features within the nucleic acid codes or polypeptide codeswith the computer program.

A nucleic acid sequence as set forth in SEQ ID NO: 1, and sequencessubstantially identical thereto, or a polypeptide sequence as set forthin SEQ ID NO: 2, and sequences substantially identical thereto, may bestored and manipulated in a variety of data processor programs in avariety of formats. For example, a nucleic acid sequence as set forth inSEQ ID NO: 1, and sequences substantially identical thereto, or apolypeptide sequence as set forth in SEQ ID NO: 2, and sequencessubstantially identical thereto, may be stored as text in a wordprocessing file, such as MicrosoftWORD or WORDPERFECT or as an ASCIIfile in a variety of database programs familiar to those of skill in theart, such as DB2, SYBASE, or ORACLE. In addition, many computer programsand databases may be used as sequence comparison algorithms,identifiers, or sources of reference nucleotide sequences or polypeptidesequences to be compared to a nucleic acid sequence as set forth in SEQID NO: 1, and sequences substantially identical thereto, or apolypeptide sequence as set forth in SEQ ID NO: 2, and sequencessubstantially identical thereto. The following list is intended not tolimit the invention but to provide guidance to programs and databaseswhich are useful with the nucleic acid sequences as set forth in SEQ IDNO: 1, and sequences substantially identical thereto, or the polypeptidesequences as set forth in SEQ ID NO: 2, and sequences substantiallyidentical thereto.

The programs and databases which may be used include, but are notlimited to: MacPattern (EMBL), DiscoveryBase (Molecular ApplicationsGroup), GeneMine (Molecular Applications Group), Look (MolecularApplications Group), MacLook (Molecular Applications Group), BLAST andBLAST2 (NCBI), BLASTN and BLASTX (Altschul et al, J. Mol. Biol. 215:403,1990), FASTA (Pearson and Lipman, Proc. Natl. Acad. Sci. USA, 85:2444,1988), FASTDB (Brutlag et al. Comp. App. Biosci. 6:237-245, 1990),Catalyst (Molecular Simulations Inc.), Catalyst/SHAPE (MolecularSimulations Inc.), Cerius².DBAccess (Molecular Simulations Inc.),HypoGen (Molecular Simulations Inc.), Insight II, (Molecular SimulationsInc.), Discover (Molecular Simulations Inc.), CHARMm (MolecularSimulations Inc.), Felix (Molecular Simulations Inc.), DelPhi,(Molecular Simulations Inc.), QuanteMM, (Molecular Simulations Inc.),Homology (Molecular Simulations Inc.), Modeler (Molecular SimulationsInc.), ISIS (Molecular Simulations Inc.), Quanta/Protein Design(Molecular Simulations Inc.), WebLab (Molecular Simulations Inc.),WebLab Diversity Explorer (Molecular Simulations Inc.), Gene Explorer(Molecular Simulations Inc.), SeqFold (Molecular Simulations Inc.), theMDL Available Chemicals Directory database, the MDL Drug Data Reportdata base, the Comprehensive Medicinal Chemistry database, Derwents'sWorld Drug Index database, the BioByteMasterFile database, the Genbankdatabase, and the Genseqn database. Many other programs and data baseswould be apparent to one of skill in the art given the presentdisclosure.

Motifs which may be detected using the above programs include sequencesencoding leucine zippers, helix-turn-helix motifs, glycosylation sites,ubiquitination sites, alpha helices, and beta sheets, signal sequencesencoding signal peptides which direct the secretion of the encodedproteins, sequences implicated in transcription regulation such ashomeoboxes, acidic stretches, enzymatic active sites, substrate bindingsites, and enzymatic cleavage sites.

The invention will be further described with reference to the followingexamples; however, it is to be understood that the invention is notlimited to such examples.

Example 1

Optimization tests were conducted to determine the most favorableconditions for utilizing the DNA polymerase of SEQ ID NO: 2 forpolymerase activity in PCR at temperatures in the range from 85° C. to95° C. The parameters tested were buffer, pH, salt and saltconcentration, Mg ion source, detergent and detergent concentration.

The buffers tested were Tris-HCl, Tris-HOAc, phosphate buffer, Bicine,HEPES, MOPS, and TAPS. The most ideal buffer was Tris HCl.

The pH range tested was from 7.5 to 10.0. The most ideal pH was 10.0.

The salts tested were NaCl, NaOAc, KCl, (NH₄)₂SO₄, NH₄OAc, and LiCl atconcentrations from 5 mM to 200 mM. The most favorable salt was 25 mMNaOAc.

The magnesium ion sources tested were MgCl₂, Mg(OAc)₂, MgSO₄ atconcentrations from 0.5 mM to 5 mM. The most favorable of these was 2 to2.5 mM Mg(KOAc)₂.

The detergents tested were NP-40, Tween-20®, and Triton X-100®detergents at concentrations of 0.001 T to 0.5% by volume. The bestcondition was 0.002% concentration of a mixture of NP-40 and Tween-20detergents.

In view of these results, it was concluded that the most favorablebuffer for conducting PCR using the DNA polymerase of SEQ ID NO:2utilizes 60 mM Tris-HCl, pH 10.0, 25 mM NaOAc, 2 mM Mg(OAc)2, and 0.002%NP-40/Tween-20.

While the invention has been described in detail with reference tocertain preferred embodiments thereof, it will be understood thatmodifications and variations are within the spirit and scope of thatwhich is described and claimed.

1. An isolated, synthetic or recombinant nucleic acid comprising (a) aconsecutive sequence having at least 95% sequence identity to thesequence of SEQ ID NO:1 and encoding a polypeptide having polymeraseactivity, or (b) sequences fully complementary to the full length of(a).
 2. The isolated, synthetic or recombinant nucleic acid of claim 1,wherein the polypeptide has polymerase activity at a temperature in arange from about 90° C. to 113° C.
 3. The isolated, synthetic orrecombinant nucleic acid of claim 2, wherein the polymerase activity isretained at the temperature for four or more hours.
 4. The isolated,synthetic or recombinant nucleic acid of claim 1, comprising thesequence as set forth in SEQ ID NO:1, or, sequences fully complementaryto the full length thereof.
 5. The isolated, synthetic or recombinantnucleic acid of claim 1, wherein the sequence identity is determined byanalysis with a sequence comparison algorithm.
 6. An isolated, syntheticor recombinant nucleic acid comprising (a) a sequence that encodes apolypeptide having polymerase activity having at least 97% sequenceidentity to SEQ ID NO:1 or (b) a sequence fully complementary to thefull length of the sequence of (a).
 7. An isolated, synthetic orrecombinant nucleic acid comprising (a) a sequence that encodes apolypeptide having polymerase activity having at least 99% sequenceidentity to SEQ ID NO:1, or, (b) a sequence fully complementary to thefull length of the sequence of (a).
 8. The isolated, synthetic orrecombinant nucleic acid of claim 5, wherein the sequence comparisonalgorithm is FASTA version 3.0t78 with the default parameters.
 9. Anisolated, synthetic or recombinant nucleic acid comprising (a) asequence that encodes a polypeptide having polymerase activity, whereinthe polymerase-encoding sequence comprises SEQ ID NO:1, or, (b) asequence fully complementary to the full length of the nucleic acidsequence (a).
 10. An isolated, synthetic or recombinant nucleic acidencoding a polypeptide having polymerase activity and comprising thesequence as set forth in SEQ ID NO:2.
 11. The isolated, synthetic orrecombinant nucleic acid of claim 1, wherein the polypeptide haspolymerase activity at a temperature up to 150° C.
 12. The isolated,synthetic or recombinant nucleic acid of claim 1, wherein the polymeraseactivity comprises DNA polymerase activity.
 13. The isolated, syntheticor recombinant nucleic acid of claim 1, wherein the polymerase activitycomprises 3′-5′ exonuclease activity.
 14. The isolated, synthetic orrecombinant nucleic acid of claim 1, wherein the polymerase lacks a3′-5′ exonuclease activity.
 15. The isolated, synthetic or recombinantnucleic acid of claim 1, wherein the polypeptide has polymerase activityin salinity conditions from 5 mM to 200 mM salt.
 16. The isolated,synthetic or recombinant nucleic acid of claim 1, wherein the nucleicacid further comprises an expression vector.
 17. The isolated, syntheticor recombinant nucleic acid of claim 16, wherein the expression vectorcomprises a viral particle, a baculovirus, a phage, a plasmid, a cosmid,a fosmid, a bacterial artificial chromosome, a viral DNA or a P1-basedartificial chromosome.
 18. A method for making a polypeptide comprising:(a) providing a nucleic acid having a sequence set forth in claim 1 orclaim 9; and (b) expressing the sequence, thereby expressing the encodedpolypeptide.
 19. The method of claim 18, wherein the nucleic acidfurther comprises an expression vector.
 20. The method of claim 18,further comprising inserting the nucleic acid into a host cell andexpressing the sequence in the host cell.
 21. The method of claim 20,wherein the host cell is a prokaryotic or a eukaryotic cell.
 22. Themethod of claim 20, wherein the host cell is a yeast cell, a bacterialcell, a mammalian cell, a fungal cell, an insect cell or a plant cell.23. An isolated, synthetic or recombinant nucleic acid comprising (a) asequence having at least 95% sequence identity to SEQ ID NO:1 andencoding a polypeptide having polymerase activity, wherein thepolypeptide has the sequence as set forth in SEQ ID NO: 2, and at leastone conservative amino acid residue substitution, or (b) a sequencefully complementary to the full length of (a), wherein the conservativeamino acid residue substitution comprises substitution of one amino acidfor another of the same class.
 24. The isolated, synthetic orrecombinant nucleic acid of claim 23, wherein the at least oneconservative amino acid residue substitution comprises substitution ofone hydrophobic amino acid for another, or substitution of one polaramino acid for another.
 25. The isolated, synthetic or recombinantnucleic acid of claim 24, wherein the at least one conservativehydrophobic amino acid residue substitution comprises substitution of atleast one isoleucine, valine, leucine or methionine, for another. 26.The isolated, synthetic or recombinant nucleic acid of claim 24, whereinthe at least one polar amino acid residue substitution comprisessubstitution of arginine for lysine, glutamic acid for aspartic acid, orglutamine for asparagine.
 27. An isolated, synthetic or recombinantnucleic acid that encodes a polymerase, wherein the polymerase comprisesan amino acid sequence having at least 95% sequence identity to SEQ IDNO:2, or a sequence fully complementary to the full length of saidnucleic acid.
 28. An isolated, synthetic or recombinant nucleic acidthat encodes a polymerase, wherein the polymerase comprises an aminoacid sequence that is a variant of SEQ ID NO:2, and the variantpolymerase sequence has at least 97% sequence identity to SEQ ID NO:2,or a sequence fully complementary to the full length of said nucleicacid.